/*
 * The little filesystem
 *
 * Copyright (c) 2017, Arm Limited. All rights reserved.
 * SPDX-License-Identifier: BSD-3-Clause
 */
#include "lfs.h"
#include "lfs_util.h"

#define LFS_BLOCK_NULL ((lfs_block_t)-1)
#define LFS_BLOCK_INLINE ((lfs_block_t)-2)

/// Caching block device operations ///
static inline void lfs_cache_drop(lfs_t *lfs, lfs_cache_t *rcache)
{
	// do not zero, cheaper if cache is readonly or only going to be
	// written with identical data (during relocates)
	(void)lfs;
	rcache->block = LFS_BLOCK_NULL;
}

static inline void lfs_cache_zero(lfs_t *lfs, lfs_cache_t *pcache)
{
	// zero to avoid information leak
	memset(pcache->buffer, 0xff, lfs->cfg->cache_size);
	pcache->block = LFS_BLOCK_NULL;
}

static int lfs_bd_read(lfs_t *lfs,
					   const lfs_cache_t *pcache,
					   lfs_cache_t *rcache,
					   lfs_size_t hint,
					   lfs_block_t block,
					   lfs_off_t off,
					   void *buffer,
					   lfs_size_t size)
{
	uint8_t *data = buffer;
	if(block >= lfs->cfg->block_count || off + size > lfs->cfg->block_size)
	{
		return LFS_ERR_CORRUPT;
	}

	while(size > 0)
	{
		lfs_size_t diff = size;

		if(pcache && block == pcache->block && off < pcache->off + pcache->size)
		{
			if(off >= pcache->off)
			{
				// is already in pcache?
				diff = lfs_min(diff, pcache->size - (off - pcache->off));
				memcpy(data, &pcache->buffer[off - pcache->off], diff);

				data += diff;
				off += diff;
				size -= diff;
				continue;
			}

			// pcache takes priority
			diff = lfs_min(diff, pcache->off - off);
		}

		if(block == rcache->block && off < rcache->off + rcache->size)
		{
			if(off >= rcache->off)
			{
				// is already in rcache?
				diff = lfs_min(diff, rcache->size - (off - rcache->off));
				memcpy(data, &rcache->buffer[off - rcache->off], diff);

				data += diff;
				off += diff;
				size -= diff;
				continue;
			}

			// rcache takes priority
			diff = lfs_min(diff, rcache->off - off);
		}

		if(size >= hint && off % lfs->cfg->read_size == 0 && size >= lfs->cfg->read_size)
		{
			// bypass cache?
			diff = lfs_aligndown(diff, lfs->cfg->read_size);
			int err = lfs->cfg->read(lfs->cfg, block, off, data, diff);
			if(err)
			{
				return err;
			}

			data += diff;
			off += diff;
			size -= diff;
			continue;
		}

		// load to cache, first condition can no longer fail
		LFS_ASSERT(block < lfs->cfg->block_count);
		rcache->block = block;
		rcache->off = lfs_aligndown(off, lfs->cfg->read_size);
		rcache->size =
			lfs_min(lfs_min(lfs_alignup(off + hint, lfs->cfg->read_size), lfs->cfg->block_size) - rcache->off,
					lfs->cfg->cache_size);
		int err = lfs->cfg->read(lfs->cfg, rcache->block, rcache->off, rcache->buffer, rcache->size);
		LFS_ASSERT(err <= 0);
		if(err)
		{
			return err;
		}
	}

	return 0;
}

enum
{
	LFS_CMP_EQ = 0,
	LFS_CMP_LT = 1,
	LFS_CMP_GT = 2,
};

static int lfs_bd_cmp(lfs_t *lfs,
					  const lfs_cache_t *pcache,
					  lfs_cache_t *rcache,
					  lfs_size_t hint,
					  lfs_block_t block,
					  lfs_off_t off,
					  const void *buffer,
					  lfs_size_t size)
{
	const uint8_t *data = buffer;

	for(lfs_off_t i = 0; i < size; i++)
	{
		uint8_t dat;
		int err = lfs_bd_read(lfs, pcache, rcache, hint - i, block, off + i, &dat, 1);
		if(err)
		{
			return err;
		}

		if(dat != data[i])
		{
			return (dat < data[i]) ? LFS_CMP_LT : LFS_CMP_GT;
		}
	}

	return LFS_CMP_EQ;
}

static int lfs_bd_flush(lfs_t *lfs, lfs_cache_t *pcache, lfs_cache_t *rcache, bool validate)
{
	if(pcache->block != LFS_BLOCK_NULL && pcache->block != LFS_BLOCK_INLINE)
	{
		LFS_ASSERT(pcache->block < lfs->cfg->block_count);
		lfs_size_t diff = lfs_alignup(pcache->size, lfs->cfg->prog_size);
		int err = lfs->cfg->prog(lfs->cfg, pcache->block, pcache->off, pcache->buffer, diff);
		LFS_ASSERT(err <= 0);
		if(err)
		{
			return err;
		}

		if(validate)
		{
			// check data on disk
			lfs_cache_drop(lfs, rcache);
			int res = lfs_bd_cmp(lfs, NULL, rcache, diff, pcache->block, pcache->off, pcache->buffer, diff);
			if(res < 0)
			{
				return res;
			}

			if(res != LFS_CMP_EQ)
			{
				return LFS_ERR_CORRUPT;
			}
		}

		lfs_cache_zero(lfs, pcache);
	}

	return 0;
}

static int lfs_bd_sync(lfs_t *lfs, lfs_cache_t *pcache, lfs_cache_t *rcache, bool validate)
{
	lfs_cache_drop(lfs, rcache);

	int err = lfs_bd_flush(lfs, pcache, rcache, validate);
	if(err)
	{
		return err;
	}

	err = lfs->cfg->sync(lfs->cfg);
	LFS_ASSERT(err <= 0);
	return err;
}

static int lfs_bd_prog(lfs_t *lfs,
					   lfs_cache_t *pcache,
					   lfs_cache_t *rcache,
					   bool validate,
					   lfs_block_t block,
					   lfs_off_t off,
					   const void *buffer,
					   lfs_size_t size)
{
	const uint8_t *data = buffer;
	LFS_ASSERT(block == LFS_BLOCK_INLINE || block < lfs->cfg->block_count);
	LFS_ASSERT(off + size <= lfs->cfg->block_size);

	while(size > 0)
	{
		if(block == pcache->block && off >= pcache->off && off < pcache->off + lfs->cfg->cache_size)
		{
			// already fits in pcache?
			lfs_size_t diff = lfs_min(size, lfs->cfg->cache_size - (off - pcache->off));
			memcpy(&pcache->buffer[off - pcache->off], data, diff);

			data += diff;
			off += diff;
			size -= diff;

			pcache->size = lfs_max(pcache->size, off - pcache->off);
			if(pcache->size == lfs->cfg->cache_size)
			{
				// eagerly flush out pcache if we fill up
				int err = lfs_bd_flush(lfs, pcache, rcache, validate);
				if(err)
				{
					return err;
				}
			}

			continue;
		}

		// pcache must have been flushed, either by programming and
		// entire block or manually flushing the pcache
		LFS_ASSERT(pcache->block == LFS_BLOCK_NULL);

		// prepare pcache, first condition can no longer fail
		pcache->block = block;
		pcache->off = lfs_aligndown(off, lfs->cfg->prog_size);
		pcache->size = 0;
	}

	return 0;
}

static int lfs_bd_erase(lfs_t *lfs, lfs_block_t block)
{
	LFS_ASSERT(block < lfs->cfg->block_count);
	int err = lfs->cfg->erase(lfs->cfg, block);
	LFS_ASSERT(err <= 0);
	return err;
}


/// Small type-level utilities ///
// operations on block pairs
static inline void lfs_pair_swap(lfs_block_t pair[2])
{
	lfs_block_t t = pair[0];
	pair[0] = pair[1];
	pair[1] = t;
}

static inline bool lfs_pair_isnull(const lfs_block_t pair[2])
{
	return pair[0] == LFS_BLOCK_NULL || pair[1] == LFS_BLOCK_NULL;
}

static inline int lfs_pair_cmp(const lfs_block_t paira[2], const lfs_block_t pairb[2])
{
	return !(paira[0] == pairb[0] || paira[1] == pairb[1] || paira[0] == pairb[1] || paira[1] == pairb[0]);
}

static inline bool lfs_pair_sync(const lfs_block_t paira[2], const lfs_block_t pairb[2])
{
	return (paira[0] == pairb[0] && paira[1] == pairb[1]) || (paira[0] == pairb[1] && paira[1] == pairb[0]);
}

static inline void lfs_pair_fromle32(lfs_block_t pair[2])
{
	pair[0] = lfs_fromle32(pair[0]);
	pair[1] = lfs_fromle32(pair[1]);
}

static inline void lfs_pair_tole32(lfs_block_t pair[2])
{
	pair[0] = lfs_tole32(pair[0]);
	pair[1] = lfs_tole32(pair[1]);
}

// operations on 32-bit entry tags
typedef uint32_t lfs_tag_t;
typedef int32_t lfs_stag_t;

#define LFS_MKTAG(type, id, size) (((lfs_tag_t)(type) << 20) | ((lfs_tag_t)(id) << 10) | (lfs_tag_t)(size))

#define LFS_MKTAG_IF(cond, type, id, size) ((cond) ? LFS_MKTAG(type, id, size) : LFS_MKTAG(LFS_FROM_NOOP, 0, 0))

#define LFS_MKTAG_IF_ELSE(cond, type1, id1, size1, type2, id2, size2) \
	((cond) ? LFS_MKTAG(type1, id1, size1) : LFS_MKTAG(type2, id2, size2))

static inline bool lfs_tag_isvalid(lfs_tag_t tag)
{
	return !(tag & 0x80000000);
}

static inline bool lfs_tag_isdelete(lfs_tag_t tag)
{
	return ((int32_t)(tag << 22) >> 22) == -1;
}

static inline uint16_t lfs_tag_type1(lfs_tag_t tag)
{
	return (tag & 0x70000000) >> 20;
}

static inline uint16_t lfs_tag_type3(lfs_tag_t tag)
{
	return (tag & 0x7ff00000) >> 20;
}

static inline uint8_t lfs_tag_chunk(lfs_tag_t tag)
{
	return (tag & 0x0ff00000) >> 20;
}

static inline int8_t lfs_tag_splice(lfs_tag_t tag)
{
	return (int8_t)lfs_tag_chunk(tag);
}

static inline uint16_t lfs_tag_id(lfs_tag_t tag)
{
	return (tag & 0x000ffc00) >> 10;
}

static inline lfs_size_t lfs_tag_size(lfs_tag_t tag)
{
	return tag & 0x000003ff;
}

static inline lfs_size_t lfs_tag_dsize(lfs_tag_t tag)
{
	return sizeof(tag) + lfs_tag_size(tag + lfs_tag_isdelete(tag));
}

// operations on attributes in attribute lists
struct lfs_mattr
{
	lfs_tag_t tag;
	const void *buffer;
};

struct lfs_diskoff
{
	lfs_block_t block;
	lfs_off_t off;
};

#define LFS_MKATTRS(...) \
	(struct lfs_mattr[]){ __VA_ARGS__ }, sizeof((struct lfs_mattr[]){ __VA_ARGS__ }) / sizeof(struct lfs_mattr)

// operations on global state
static inline void lfs_gstate_xor(lfs_gstate_t *a, const lfs_gstate_t *b)
{
	for(int i = 0; i < 3; i++)
	{
		((uint32_t *)a)[i] ^= ((const uint32_t *)b)[i];
	}
}

static inline bool lfs_gstate_iszero(const lfs_gstate_t *a)
{
	for(int i = 0; i < 3; i++)
	{
		if(((uint32_t *)a)[i] != 0)
		{
			return false;
		}
	}
	return true;
}

static inline bool lfs_gstate_hasorphans(const lfs_gstate_t *a)
{
	return lfs_tag_size(a->tag);
}

static inline uint8_t lfs_gstate_getorphans(const lfs_gstate_t *a)
{
	return lfs_tag_size(a->tag);
}

static inline bool lfs_gstate_hasmove(const lfs_gstate_t *a)
{
	return lfs_tag_type1(a->tag);
}

static inline bool lfs_gstate_hasmovehere(const lfs_gstate_t *a, const lfs_block_t *pair)
{
	return lfs_tag_type1(a->tag) && lfs_pair_cmp(a->pair, pair) == 0;
}

static inline void lfs_gstate_fromle32(lfs_gstate_t *a)
{
	a->tag = lfs_fromle32(a->tag);
	a->pair[0] = lfs_fromle32(a->pair[0]);
	a->pair[1] = lfs_fromle32(a->pair[1]);
}

static inline void lfs_gstate_tole32(lfs_gstate_t *a)
{
	a->tag = lfs_tole32(a->tag);
	a->pair[0] = lfs_tole32(a->pair[0]);
	a->pair[1] = lfs_tole32(a->pair[1]);
}

// other endianness operations
static void lfs_ctz_fromle32(struct lfs_ctz *ctz)
{
	ctz->head = lfs_fromle32(ctz->head);
	ctz->size = lfs_fromle32(ctz->size);
}

static void lfs_ctz_tole32(struct lfs_ctz *ctz)
{
	ctz->head = lfs_tole32(ctz->head);
	ctz->size = lfs_tole32(ctz->size);
}

static inline void lfs_superblock_fromle32(lfs_superblock_t *superblock)
{
	superblock->version = lfs_fromle32(superblock->version);
	superblock->block_size = lfs_fromle32(superblock->block_size);
	superblock->block_count = lfs_fromle32(superblock->block_count);
	superblock->name_max = lfs_fromle32(superblock->name_max);
	superblock->file_max = lfs_fromle32(superblock->file_max);
	superblock->attr_max = lfs_fromle32(superblock->attr_max);
}

static inline void lfs_superblock_tole32(lfs_superblock_t *superblock)
{
	superblock->version = lfs_tole32(superblock->version);
	superblock->block_size = lfs_tole32(superblock->block_size);
	superblock->block_count = lfs_tole32(superblock->block_count);
	superblock->name_max = lfs_tole32(superblock->name_max);
	superblock->file_max = lfs_tole32(superblock->file_max);
	superblock->attr_max = lfs_tole32(superblock->attr_max);
}


/// Internal operations predeclared here ///
static int lfs_dir_commit(lfs_t *lfs, lfs_mdir_t *dir, const struct lfs_mattr *attrs, int attrcount);
static int lfs_dir_compact(lfs_t *lfs,
						   lfs_mdir_t *dir,
						   const struct lfs_mattr *attrs,
						   int attrcount,
						   lfs_mdir_t *source,
						   uint16_t begin,
						   uint16_t end);
static int lfs_file_outline(lfs_t *lfs, lfs_file_t *file);
static int lfs_file_flush(lfs_t *lfs, lfs_file_t *file);
static void lfs_fs_preporphans(lfs_t *lfs, int8_t orphans);
static void lfs_fs_prepmove(lfs_t *lfs, uint16_t id, const lfs_block_t pair[2]);
static int lfs_fs_pred(lfs_t *lfs, const lfs_block_t dir[2], lfs_mdir_t *pdir);
static lfs_stag_t lfs_fs_parent(lfs_t *lfs, const lfs_block_t dir[2], lfs_mdir_t *parent);
static int lfs_fs_relocate(lfs_t *lfs, const lfs_block_t oldpair[2], lfs_block_t newpair[2]);
int lfs_fs_traverseraw(lfs_t *lfs, int (*cb)(void *data, lfs_block_t block), void *data, bool includeorphans);
static int lfs_fs_forceconsistency(lfs_t *lfs);
static int lfs_deinit(lfs_t *lfs);
#ifdef LFS_MIGRATE
static int lfs1_traverse(lfs_t *lfs, int (*cb)(void *, lfs_block_t), void *data);
#endif

/// Block allocator ///
static int lfs_alloc_lookahead(void *p, lfs_block_t block)
{
	lfs_t *lfs = (lfs_t *)p;
	lfs_block_t off = ((block - lfs->free.off) + lfs->cfg->block_count) % lfs->cfg->block_count;

	if(off < lfs->free.size)
	{
		lfs->free.buffer[off / 32] |= 1U << (off % 32);
	}

	return 0;
}

static void lfs_alloc_ack(lfs_t *lfs)
{
	lfs->free.ack = lfs->cfg->block_count;
}

// Invalidate the lookahead buffer. This is done during mounting and
// failed traversals
static void lfs_alloc_reset(lfs_t *lfs)
{
	lfs->free.off = lfs->seed % lfs->cfg->block_size;
	lfs->free.size = 0;
	lfs->free.i = 0;
	lfs_alloc_ack(lfs);
}

static int lfs_alloc(lfs_t *lfs, lfs_block_t *block)
{
	while(true)
	{
		while(lfs->free.i != lfs->free.size)
		{
			lfs_block_t off = lfs->free.i;
			lfs->free.i += 1;
			lfs->free.ack -= 1;

			if(!(lfs->free.buffer[off / 32] & (1U << (off % 32))))
			{
				// found a free block
				*block = (lfs->free.off + off) % lfs->cfg->block_count;

				// eagerly find next off so an alloc ack can
				// discredit old lookahead blocks
				while(lfs->free.i != lfs->free.size
					  && (lfs->free.buffer[lfs->free.i / 32] & (1U << (lfs->free.i % 32))))
				{
					lfs->free.i += 1;
					lfs->free.ack -= 1;
				}

				return 0;
			}
		}

		// check if we have looked at all blocks since last ack
		if(lfs->free.ack == 0)
		{
			LFS_ERROR("No more free space %" PRIu32, lfs->free.i + lfs->free.off);
			return LFS_ERR_NOSPC;
		}

		lfs->free.off = (lfs->free.off + lfs->free.size) % lfs->cfg->block_count;
		lfs->free.size = lfs_min(8 * lfs->cfg->lookahead_size, lfs->free.ack);
		lfs->free.i = 0;

		// find mask of free blocks from tree
		memset(lfs->free.buffer, 0, lfs->cfg->lookahead_size);
		int err = lfs_fs_traverseraw(lfs, lfs_alloc_lookahead, lfs, true);
		if(err)
		{
			lfs_alloc_reset(lfs);
			return err;
		}
	}
}

/// Metadata pair and directory operations ///
static lfs_stag_t lfs_dir_getslice(
	lfs_t *lfs, const lfs_mdir_t *dir, lfs_tag_t gmask, lfs_tag_t gtag, lfs_off_t goff, void *gbuffer, lfs_size_t gsize)
{
	lfs_off_t off = dir->off;
	lfs_tag_t ntag = dir->etag;
	lfs_stag_t gdiff = 0;

	if(lfs_gstate_hasmovehere(&lfs->gdisk, dir->pair) && lfs_tag_id(gmask) != 0
	   && lfs_tag_id(lfs->gdisk.tag) <= lfs_tag_id(gtag))
	{
		// synthetic moves
		gdiff -= LFS_MKTAG(0, 1, 0);
	}

	// iterate over dir block backwards (for faster lookups)
	while(off >= sizeof(lfs_tag_t) + lfs_tag_dsize(ntag))
	{
		off -= lfs_tag_dsize(ntag);
		lfs_tag_t tag = ntag;
		int err = lfs_bd_read(lfs, NULL, &lfs->rcache, sizeof(ntag), dir->pair[0], off, &ntag, sizeof(ntag));
		if(err)
		{
			return err;
		}

		ntag = (lfs_frombe32(ntag) ^ tag) & 0x7fffffff;

		if(lfs_tag_id(gmask) != 0 && lfs_tag_type1(tag) == LFS_TYPE_SPLICE
		   && lfs_tag_id(tag) <= lfs_tag_id(gtag - gdiff))
		{
			if(tag == (LFS_MKTAG(LFS_TYPE_CREATE, 0, 0) | (LFS_MKTAG(0, 0x3ff, 0) & (gtag - gdiff))))
			{
				// found where we were created
				return LFS_ERR_NOENT;
			}

			// move around splices
			gdiff += LFS_MKTAG(0, lfs_tag_splice(tag), 0);
		}

		if((gmask & tag) == (gmask & (gtag - gdiff)))
		{
			if(lfs_tag_isdelete(tag))
			{
				return LFS_ERR_NOENT;
			}

			lfs_size_t diff = lfs_min(lfs_tag_size(tag), gsize);
			err = lfs_bd_read(lfs, NULL, &lfs->rcache, diff, dir->pair[0], off + sizeof(tag) + goff, gbuffer, diff);
			if(err)
			{
				return err;
			}

			memset((uint8_t *)gbuffer + diff, 0, gsize - diff);

			return tag + gdiff;
		}
	}

	return LFS_ERR_NOENT;
}

static lfs_stag_t lfs_dir_get(lfs_t *lfs, const lfs_mdir_t *dir, lfs_tag_t gmask, lfs_tag_t gtag, void *buffer)
{
	return lfs_dir_getslice(lfs, dir, gmask, gtag, 0, buffer, lfs_tag_size(gtag));
}

static int lfs_dir_getread(lfs_t *lfs,
						   const lfs_mdir_t *dir,
						   const lfs_cache_t *pcache,
						   lfs_cache_t *rcache,
						   lfs_size_t hint,
						   lfs_tag_t gmask,
						   lfs_tag_t gtag,
						   lfs_off_t off,
						   void *buffer,
						   lfs_size_t size)
{
	uint8_t *data = buffer;
	if(off + size > lfs->cfg->block_size)
	{
		return LFS_ERR_CORRUPT;
	}

	while(size > 0)
	{
		lfs_size_t diff = size;

		if(pcache && pcache->block == LFS_BLOCK_INLINE && off < pcache->off + pcache->size)
		{
			if(off >= pcache->off)
			{
				// is already in pcache?
				diff = lfs_min(diff, pcache->size - (off - pcache->off));
				memcpy(data, &pcache->buffer[off - pcache->off], diff);

				data += diff;
				off += diff;
				size -= diff;
				continue;
			}

			// pcache takes priority
			diff = lfs_min(diff, pcache->off - off);
		}

		if(rcache->block == LFS_BLOCK_INLINE && off < rcache->off + rcache->size)
		{
			if(off >= rcache->off)
			{
				// is already in rcache?
				diff = lfs_min(diff, rcache->size - (off - rcache->off));
				memcpy(data, &rcache->buffer[off - rcache->off], diff);

				data += diff;
				off += diff;
				size -= diff;
				continue;
			}

			// rcache takes priority
			diff = lfs_min(diff, rcache->off - off);
		}

		// load to cache, first condition can no longer fail
		rcache->block = LFS_BLOCK_INLINE;
		rcache->off = lfs_aligndown(off, lfs->cfg->read_size);
		rcache->size = lfs_min(lfs_alignup(off + hint, lfs->cfg->read_size), lfs->cfg->cache_size);
		int err = lfs_dir_getslice(lfs, dir, gmask, gtag, rcache->off, rcache->buffer, rcache->size);
		if(err < 0)
		{
			return err;
		}
	}

	return 0;
}

static int lfs_dir_traverse_filter(void *p, lfs_tag_t tag, const void *buffer)
{
	lfs_tag_t *filtertag = p;
	(void)buffer;

	// which mask depends on unique bit in tag structure
	uint32_t mask = (tag & LFS_MKTAG(0x100, 0, 0)) ? LFS_MKTAG(0x7ff, 0x3ff, 0) : LFS_MKTAG(0x700, 0x3ff, 0);

	// check for redundancy
	if((mask & tag) == (mask & *filtertag) || lfs_tag_isdelete(*filtertag)
	   || (LFS_MKTAG(0x7ff, 0x3ff, 0) & tag)
			  == (LFS_MKTAG(LFS_TYPE_DELETE, 0, 0) | (LFS_MKTAG(0, 0x3ff, 0) & *filtertag)))
	{
		return true;
	}

	// check if we need to adjust for created/deleted tags
	if(lfs_tag_type1(tag) == LFS_TYPE_SPLICE && lfs_tag_id(tag) <= lfs_tag_id(*filtertag))
	{
		*filtertag += LFS_MKTAG(0, lfs_tag_splice(tag), 0);
	}

	return false;
}

static int lfs_dir_traverse(lfs_t *lfs,
							const lfs_mdir_t *dir,
							lfs_off_t off,
							lfs_tag_t ptag,
							const struct lfs_mattr *attrs,
							int attrcount,
							lfs_tag_t tmask,
							lfs_tag_t ttag,
							uint16_t begin,
							uint16_t end,
							int16_t diff,
							int (*cb)(void *data, lfs_tag_t tag, const void *buffer),
							void *data)
{
	// iterate over directory and attrs
	while(true)
	{
		lfs_tag_t tag;
		const void *buffer;
		struct lfs_diskoff disk;
		if(off + lfs_tag_dsize(ptag) < dir->off)
		{
			off += lfs_tag_dsize(ptag);
			int err = lfs_bd_read(lfs, NULL, &lfs->rcache, sizeof(tag), dir->pair[0], off, &tag, sizeof(tag));
			if(err)
			{
				return err;
			}

			tag = (lfs_frombe32(tag) ^ ptag) | 0x80000000;
			disk.block = dir->pair[0];
			disk.off = off + sizeof(lfs_tag_t);
			buffer = &disk;
			ptag = tag;
		}
		else if(attrcount > 0)
		{
			tag = attrs[0].tag;
			buffer = attrs[0].buffer;
			attrs += 1;
			attrcount -= 1;
		}
		else
		{
			return 0;
		}

		lfs_tag_t mask = LFS_MKTAG(0x7ff, 0, 0);
		if((mask & tmask & tag) != (mask & tmask & ttag))
		{
			continue;
		}

		// do we need to filter? inlining the filtering logic here allows
		// for some minor optimizations
		if(lfs_tag_id(tmask) != 0)
		{
			// scan for duplicates and update tag based on creates/deletes
			int filter =
				lfs_dir_traverse(lfs, dir, off, ptag, attrs, attrcount, 0, 0, 0, 0, 0, lfs_dir_traverse_filter, &tag);
			if(filter < 0)
			{
				return filter;
			}

			if(filter)
			{
				continue;
			}

			// in filter range?
			if(!(lfs_tag_id(tag) >= begin && lfs_tag_id(tag) < end))
			{
				continue;
			}
		}

		// handle special cases for mcu-side operations
		if(lfs_tag_type3(tag) == LFS_FROM_NOOP)
		{
			// do nothing
		}
		else if(lfs_tag_type3(tag) == LFS_FROM_MOVE)
		{
			uint16_t fromid = lfs_tag_size(tag);
			uint16_t toid = lfs_tag_id(tag);
			int err = lfs_dir_traverse(lfs,
									   buffer,
									   0,
									   0xffffffff,
									   NULL,
									   0,
									   LFS_MKTAG(0x600, 0x3ff, 0),
									   LFS_MKTAG(LFS_TYPE_STRUCT, 0, 0),
									   fromid,
									   fromid + 1,
									   toid - fromid + diff,
									   cb,
									   data);
			if(err)
			{
				return err;
			}
		}
		else if(lfs_tag_type3(tag) == LFS_FROM_USERATTRS)
		{
			for(unsigned i = 0; i < lfs_tag_size(tag); i++)
			{
				const struct lfs_attr *a = buffer;
				int err =
					cb(data, LFS_MKTAG(LFS_TYPE_USERATTR + a[i].type, lfs_tag_id(tag) + diff, a[i].size), a[i].buffer);
				if(err)
				{
					return err;
				}
			}
		}
		else
		{
			int err = cb(data, tag + LFS_MKTAG(0, diff, 0), buffer);
			if(err)
			{
				return err;
			}
		}
	}
}

static lfs_stag_t lfs_dir_fetchmatch(lfs_t *lfs,
									 lfs_mdir_t *dir,
									 const lfs_block_t pair[2],
									 lfs_tag_t fmask,
									 lfs_tag_t ftag,
									 uint16_t *id,
									 int (*cb)(void *data, lfs_tag_t tag, const void *buffer),
									 void *data)
{
	// we can find tag very efficiently during a fetch, since we're already
	// scanning the entire directory
	lfs_stag_t besttag = -1;

	// if either block address is invalid we return LFS_ERR_CORRUPT here,
	// otherwise later writes to the pair could fail
	if(pair[0] >= lfs->cfg->block_count || pair[1] >= lfs->cfg->block_count)
	{
		return LFS_ERR_CORRUPT;
	}

	// find the block with the most recent revision
	uint32_t revs[2] = { 0, 0 };
	int r = 0;
	for(int i = 0; i < 2; i++)
	{
		int err = lfs_bd_read(lfs, NULL, &lfs->rcache, sizeof(revs[i]), pair[i], 0, &revs[i], sizeof(revs[i]));
		revs[i] = lfs_fromle32(revs[i]);
		if(err && err != LFS_ERR_CORRUPT)
		{
			return err;
		}

		if(err != LFS_ERR_CORRUPT && lfs_scmp(revs[i], revs[(i + 1) % 2]) > 0)
		{
			r = i;
		}
	}

	dir->pair[0] = pair[(r + 0) % 2];
	dir->pair[1] = pair[(r + 1) % 2];
	dir->rev = revs[(r + 0) % 2];
	dir->off = 0;  // nonzero = found some commits

	// now scan tags to fetch the actual dir and find possible match
	for(int i = 0; i < 2; i++)
	{
		lfs_off_t off = 0;
		lfs_tag_t ptag = 0xffffffff;

		uint16_t tempcount = 0;
		lfs_block_t temptail[2] = { LFS_BLOCK_NULL, LFS_BLOCK_NULL };
		bool tempsplit = false;
		lfs_stag_t tempbesttag = besttag;

		dir->rev = lfs_tole32(dir->rev);
		uint32_t crc = lfs_crc(0xffffffff, &dir->rev, sizeof(dir->rev));
		dir->rev = lfs_fromle32(dir->rev);

		while(true)
		{
			// extract next tag
			lfs_tag_t tag;
			off += lfs_tag_dsize(ptag);
			int err = lfs_bd_read(lfs, NULL, &lfs->rcache, lfs->cfg->block_size, dir->pair[0], off, &tag, sizeof(tag));
			if(err)
			{
				if(err == LFS_ERR_CORRUPT)
				{
					// can't continue?
					dir->erased = false;
					break;
				}
				return err;
			}

			crc = lfs_crc(crc, &tag, sizeof(tag));
			tag = lfs_frombe32(tag) ^ ptag;

			// next commit not yet programmed or we're not in valid range
			if(!lfs_tag_isvalid(tag))
			{
				dir->erased = (lfs_tag_type1(ptag) == LFS_TYPE_CRC && dir->off % lfs->cfg->prog_size == 0);
				break;
			}
			else if(off + lfs_tag_dsize(tag) > lfs->cfg->block_size)
			{
				dir->erased = false;
				break;
			}

			ptag = tag;

			if(lfs_tag_type1(tag) == LFS_TYPE_CRC)
			{
				// check the crc attr
				uint32_t dcrc;
				err = lfs_bd_read(lfs,
								  NULL,
								  &lfs->rcache,
								  lfs->cfg->block_size,
								  dir->pair[0],
								  off + sizeof(tag),
								  &dcrc,
								  sizeof(dcrc));
				if(err)
				{
					if(err == LFS_ERR_CORRUPT)
					{
						dir->erased = false;
						break;
					}
					return err;
				}
				dcrc = lfs_fromle32(dcrc);

				if(crc != dcrc)
				{
					dir->erased = false;
					break;
				}

				// reset the next bit if we need to
				ptag ^= (lfs_tag_t)(lfs_tag_chunk(tag) & 1U) << 31;

				// toss our crc into the filesystem seed for
				// pseudorandom numbers
				lfs->seed ^= crc;

				// update with what's found so far
				besttag = tempbesttag;
				dir->off = off + lfs_tag_dsize(tag);
				dir->etag = ptag;
				dir->count = tempcount;
				dir->tail[0] = temptail[0];
				dir->tail[1] = temptail[1];
				dir->split = tempsplit;

				// reset crc
				crc = 0xffffffff;
				continue;
			}

			// crc the entry first, hopefully leaving it in the cache
			for(lfs_off_t j = sizeof(tag); j < lfs_tag_dsize(tag); j++)
			{
				uint8_t dat;
				err = lfs_bd_read(lfs, NULL, &lfs->rcache, lfs->cfg->block_size, dir->pair[0], off + j, &dat, 1);
				if(err)
				{
					if(err == LFS_ERR_CORRUPT)
					{
						dir->erased = false;
						break;
					}
					return err;
				}

				crc = lfs_crc(crc, &dat, 1);
			}

			// directory modification tags?
			if(lfs_tag_type1(tag) == LFS_TYPE_NAME)
			{
				// increase count of files if necessary
				if(lfs_tag_id(tag) >= tempcount)
				{
					tempcount = lfs_tag_id(tag) + 1;
				}
			}
			else if(lfs_tag_type1(tag) == LFS_TYPE_SPLICE)
			{
				tempcount += lfs_tag_splice(tag);

				if(tag == (LFS_MKTAG(LFS_TYPE_DELETE, 0, 0) | (LFS_MKTAG(0, 0x3ff, 0) & tempbesttag)))
				{
					tempbesttag |= 0x80000000;
				}
				else if(tempbesttag != -1 && lfs_tag_id(tag) <= lfs_tag_id(tempbesttag))
				{
					tempbesttag += LFS_MKTAG(0, lfs_tag_splice(tag), 0);
				}
			}
			else if(lfs_tag_type1(tag) == LFS_TYPE_TAIL)
			{
				tempsplit = (lfs_tag_chunk(tag) & 1);

				err = lfs_bd_read(
					lfs, NULL, &lfs->rcache, lfs->cfg->block_size, dir->pair[0], off + sizeof(tag), &temptail, 8);
				if(err)
				{
					if(err == LFS_ERR_CORRUPT)
					{
						dir->erased = false;
						break;
					}
				}
				lfs_pair_fromle32(temptail);
			}

			// found a match for our fetcher?
			if((fmask & tag) == (fmask & ftag))
			{
				int res = cb(data, tag, &(struct lfs_diskoff){ dir->pair[0], off + sizeof(tag) });
				if(res < 0)
				{
					if(res == LFS_ERR_CORRUPT)
					{
						dir->erased = false;
						break;
					}
					return res;
				}

				if(res == LFS_CMP_EQ)
				{
					// found a match
					tempbesttag = tag;
				}
				else if((LFS_MKTAG(0x7ff, 0x3ff, 0) & tag) == (LFS_MKTAG(0x7ff, 0x3ff, 0) & tempbesttag))
				{
					// found an identical tag, but contents didn't match
					// this must mean that our besttag has been overwritten
					tempbesttag = -1;
				}
				else if(res == LFS_CMP_GT && lfs_tag_id(tag) <= lfs_tag_id(tempbesttag))
				{
					// found a greater match, keep track to keep things sorted
					tempbesttag = tag | 0x80000000;
				}
			}
		}

		// consider what we have good enough
		if(dir->off > 0)
		{
			// synthetic move
			if(lfs_gstate_hasmovehere(&lfs->gdisk, dir->pair))
			{
				if(lfs_tag_id(lfs->gdisk.tag) == lfs_tag_id(besttag))
				{
					besttag |= 0x80000000;
				}
				else if(besttag != -1 && lfs_tag_id(lfs->gdisk.tag) < lfs_tag_id(besttag))
				{
					besttag -= LFS_MKTAG(0, 1, 0);
				}
			}

			// found tag? or found best id?
			if(id)
			{
				*id = lfs_min(lfs_tag_id(besttag), dir->count);
			}

			if(lfs_tag_isvalid(besttag))
			{
				return besttag;
			}
			else if(lfs_tag_id(besttag) < dir->count)
			{
				return LFS_ERR_NOENT;
			}
			else
			{
				return 0;
			}
		}

		// failed, try the other block?
		lfs_pair_swap(dir->pair);
		dir->rev = revs[(r + 1) % 2];
	}

	LFS_ERROR("Corrupted dir pair at {0x%" PRIx32 ", 0x%" PRIx32 "}", dir->pair[0], dir->pair[1]);
	return LFS_ERR_CORRUPT;
}

static int lfs_dir_fetch(lfs_t *lfs, lfs_mdir_t *dir, const lfs_block_t pair[2])
{
	// note, mask=-1, tag=-1 can never match a tag since this
	// pattern has the invalid bit set
	return (int)lfs_dir_fetchmatch(lfs, dir, pair, (lfs_tag_t)-1, (lfs_tag_t)-1, NULL, NULL, NULL);
}

static int lfs_dir_getgstate(lfs_t *lfs, const lfs_mdir_t *dir, lfs_gstate_t *gstate)
{
	lfs_gstate_t temp;
	lfs_stag_t res =
		lfs_dir_get(lfs, dir, LFS_MKTAG(0x7ff, 0, 0), LFS_MKTAG(LFS_TYPE_MOVESTATE, 0, sizeof(temp)), &temp);
	if(res < 0 && res != LFS_ERR_NOENT)
	{
		return res;
	}

	if(res != LFS_ERR_NOENT)
	{
		// xor together to find resulting gstate
		lfs_gstate_fromle32(&temp);
		lfs_gstate_xor(gstate, &temp);
	}

	return 0;
}

static int lfs_dir_getinfo(lfs_t *lfs, lfs_mdir_t *dir, uint16_t id, struct lfs_info *info)
{
	if(id == 0x3ff)
	{
		// special case for root
		strcpy(info->name, "/");
		info->type = LFS_TYPE_DIR;
		return 0;
	}

	lfs_stag_t tag =
		lfs_dir_get(lfs, dir, LFS_MKTAG(0x780, 0x3ff, 0), LFS_MKTAG(LFS_TYPE_NAME, id, lfs->name_max + 1), info->name);
	if(tag < 0)
	{
		return (int)tag;
	}

	info->type = lfs_tag_type3(tag);

	struct lfs_ctz ctz;
	tag = lfs_dir_get(lfs, dir, LFS_MKTAG(0x700, 0x3ff, 0), LFS_MKTAG(LFS_TYPE_STRUCT, id, sizeof(ctz)), &ctz);
	if(tag < 0)
	{
		return (int)tag;
	}
	lfs_ctz_fromle32(&ctz);

	if(lfs_tag_type3(tag) == LFS_TYPE_CTZSTRUCT)
	{
		info->size = ctz.size;
	}
	else if(lfs_tag_type3(tag) == LFS_TYPE_INLINESTRUCT)
	{
		info->size = lfs_tag_size(tag);
	}

	return 0;
}

struct lfs_dir_find_match
{
	lfs_t *lfs;
	const void *name;
	lfs_size_t size;
};

static int lfs_dir_find_match(void *data, lfs_tag_t tag, const void *buffer)
{
	struct lfs_dir_find_match *name = data;
	lfs_t *lfs = name->lfs;
	const struct lfs_diskoff *disk = buffer;

	// compare with disk
	lfs_size_t diff = lfs_min(name->size, lfs_tag_size(tag));
	int res = lfs_bd_cmp(lfs, NULL, &lfs->rcache, diff, disk->block, disk->off, name->name, diff);
	if(res != LFS_CMP_EQ)
	{
		return res;
	}

	// only equal if our size is still the same
	if(name->size != lfs_tag_size(tag))
	{
		return (name->size < lfs_tag_size(tag)) ? LFS_CMP_LT : LFS_CMP_GT;
	}

	// found a match!
	return LFS_CMP_EQ;
}

static lfs_stag_t lfs_dir_find(lfs_t *lfs, lfs_mdir_t *dir, const char **path, uint16_t *id)
{
	// we reduce path to a single name if we can find it
	const char *name = *path;
	if(id)
	{
		*id = 0x3ff;
	}

	// default to root dir
	lfs_stag_t tag = LFS_MKTAG(LFS_TYPE_DIR, 0x3ff, 0);
	dir->tail[0] = lfs->root[0];
	dir->tail[1] = lfs->root[1];

	while(true)
	{
	nextname:
		// skip slashes
		name += strspn(name, "/");
		lfs_size_t namelen = strcspn(name, "/");

		// skip '.' and root '..'
		if((namelen == 1 && memcmp(name, ".", 1) == 0) || (namelen == 2 && memcmp(name, "..", 2) == 0))
		{
			name += namelen;
			goto nextname;
		}

		// skip if matched by '..' in name
		const char *suffix = name + namelen;
		lfs_size_t sufflen;
		int depth = 1;
		while(true)
		{
			suffix += strspn(suffix, "/");
			sufflen = strcspn(suffix, "/");
			if(sufflen == 0)
			{
				break;
			}

			if(sufflen == 2 && memcmp(suffix, "..", 2) == 0)
			{
				depth -= 1;
				if(depth == 0)
				{
					name = suffix + sufflen;
					goto nextname;
				}
			}
			else
			{
				depth += 1;
			}

			suffix += sufflen;
		}

		// found path
		if(name[0] == '\0')
		{
			return tag;
		}

		// update what we've found so far
		*path = name;

		// only continue if we hit a directory
		if(lfs_tag_type3(tag) != LFS_TYPE_DIR)
		{
			return LFS_ERR_NOTDIR;
		}

		// grab the entry data
		if(lfs_tag_id(tag) != 0x3ff)
		{
			lfs_stag_t res = lfs_dir_get(
				lfs, dir, LFS_MKTAG(0x700, 0x3ff, 0), LFS_MKTAG(LFS_TYPE_STRUCT, lfs_tag_id(tag), 8), dir->tail);
			if(res < 0)
			{
				return res;
			}
			lfs_pair_fromle32(dir->tail);
		}

		// find entry matching name
		while(true)
		{
			tag = lfs_dir_fetchmatch(lfs,
									 dir,
									 dir->tail,
									 LFS_MKTAG(0x780, 0, 0),
									 LFS_MKTAG(LFS_TYPE_NAME, 0, namelen),
									 // are we last name?
									 (strchr(name, '/') == NULL) ? id : NULL,
									 lfs_dir_find_match,
									 &(struct lfs_dir_find_match){ lfs, name, namelen });
			if(tag < 0)
			{
				return tag;
			}

			if(tag)
			{
				break;
			}

			if(!dir->split)
			{
				return LFS_ERR_NOENT;
			}
		}

		// to next name
		name += namelen;
	}
}

// commit logic
struct lfs_commit
{
	lfs_block_t block;
	lfs_off_t off;
	lfs_tag_t ptag;
	uint32_t crc;

	lfs_off_t begin;
	lfs_off_t end;
};

static int lfs_dir_commitprog(lfs_t *lfs, struct lfs_commit *commit, const void *buffer, lfs_size_t size)
{
	int err =
		lfs_bd_prog(lfs, &lfs->pcache, &lfs->rcache, false, commit->block, commit->off, (const uint8_t *)buffer, size);
	if(err)
	{
		return err;
	}

	commit->crc = lfs_crc(commit->crc, buffer, size);
	commit->off += size;
	return 0;
}

static int lfs_dir_commitattr(lfs_t *lfs, struct lfs_commit *commit, lfs_tag_t tag, const void *buffer)
{
	// check if we fit
	lfs_size_t dsize = lfs_tag_dsize(tag);
	if(commit->off + dsize > commit->end)
	{
		return LFS_ERR_NOSPC;
	}

	// write out tag
	lfs_tag_t ntag = lfs_tobe32((tag & 0x7fffffff) ^ commit->ptag);
	int err = lfs_dir_commitprog(lfs, commit, &ntag, sizeof(ntag));
	if(err)
	{
		return err;
	}

	if(!(tag & 0x80000000))
	{
		// from memory
		err = lfs_dir_commitprog(lfs, commit, buffer, dsize - sizeof(tag));
		if(err)
		{
			return err;
		}
	}
	else
	{
		// from disk
		const struct lfs_diskoff *disk = buffer;
		for(lfs_off_t i = 0; i < dsize - sizeof(tag); i++)
		{
			// rely on caching to make this efficient
			uint8_t dat;
			err = lfs_bd_read(lfs, NULL, &lfs->rcache, dsize - sizeof(tag) - i, disk->block, disk->off + i, &dat, 1);
			if(err)
			{
				return err;
			}

			err = lfs_dir_commitprog(lfs, commit, &dat, 1);
			if(err)
			{
				return err;
			}
		}
	}

	commit->ptag = tag & 0x7fffffff;
	return 0;
}

static int lfs_dir_commitcrc(lfs_t *lfs, struct lfs_commit *commit)
{
	const lfs_off_t off1 = commit->off;
	const uint32_t crc1 = commit->crc;
	// align to program units
	const lfs_off_t end = lfs_alignup(off1 + 2 * sizeof(uint32_t), lfs->cfg->prog_size);

	// create crc tags to fill up remainder of commit, note that
	// padding is not crced, which lets fetches skip padding but
	// makes committing a bit more complicated
	while(commit->off < end)
	{
		lfs_off_t off = commit->off + sizeof(lfs_tag_t);
		lfs_off_t noff = lfs_min(end - off, 0x3fe) + off;
		if(noff < end)
		{
			noff = lfs_min(noff, end - 2 * sizeof(uint32_t));
		}

		// read erased state from next program unit
		lfs_tag_t tag = 0xffffffff;
		int err = lfs_bd_read(lfs, NULL, &lfs->rcache, sizeof(tag), commit->block, noff, &tag, sizeof(tag));
		if(err && err != LFS_ERR_CORRUPT)
		{
			return err;
		}

		// build crc tag
		bool reset = ~lfs_frombe32(tag) >> 31;
		tag = LFS_MKTAG(LFS_TYPE_CRC + reset, 0x3ff, noff - off);

		// write out crc
		uint32_t footer[2];
		footer[0] = lfs_tobe32(tag ^ commit->ptag);
		commit->crc = lfs_crc(commit->crc, &footer[0], sizeof(footer[0]));
		footer[1] = lfs_tole32(commit->crc);
		err = lfs_bd_prog(lfs, &lfs->pcache, &lfs->rcache, false, commit->block, commit->off, &footer, sizeof(footer));
		if(err)
		{
			return err;
		}

		commit->off += sizeof(tag) + lfs_tag_size(tag);
		commit->ptag = tag ^ ((lfs_tag_t)reset << 31);
		commit->crc = 0xffffffff;  // reset crc for next "commit"
	}

	// flush buffers
	int err = lfs_bd_sync(lfs, &lfs->pcache, &lfs->rcache, false);
	if(err)
	{
		return err;
	}

	// successful commit, check checksums to make sure
	lfs_off_t off = commit->begin;
	lfs_off_t noff = off1 + sizeof(uint32_t);
	while(off < end)
	{
		uint32_t crc = 0xffffffff;
		for(lfs_off_t i = off; i < noff + sizeof(uint32_t); i++)
		{
			// check against written crc, may catch blocks that
			// become readonly and match our commit size exactly
			if(i == off1 && crc != crc1)
			{
				return LFS_ERR_CORRUPT;
			}

			// leave it up to caching to make this efficient
			uint8_t dat;
			err = lfs_bd_read(lfs, NULL, &lfs->rcache, noff + sizeof(uint32_t) - i, commit->block, i, &dat, 1);
			if(err)
			{
				return err;
			}

			crc = lfs_crc(crc, &dat, 1);
		}

		// detected write error?
		if(crc != 0)
		{
			return LFS_ERR_CORRUPT;
		}

		// skip padding
		off = lfs_min(end - noff, 0x3fe) + noff;
		if(off < end)
		{
			off = lfs_min(off, end - 2 * sizeof(uint32_t));
		}
		noff = off + sizeof(uint32_t);
	}

	return 0;
}

static int lfs_dir_alloc(lfs_t *lfs, lfs_mdir_t *dir)
{
	// allocate pair of dir blocks (backwards, so we write block 1 first)
	for(int i = 0; i < 2; i++)
	{
		int err = lfs_alloc(lfs, &dir->pair[(i + 1) % 2]);
		if(err)
		{
			return err;
		}
	}

	// zero for reproducability in case initial block is unreadable
	dir->rev = 0;

	// rather than clobbering one of the blocks we just pretend
	// the revision may be valid
	int err = lfs_bd_read(lfs, NULL, &lfs->rcache, sizeof(dir->rev), dir->pair[0], 0, &dir->rev, sizeof(dir->rev));
	dir->rev = lfs_fromle32(dir->rev);
	if(err && err != LFS_ERR_CORRUPT)
	{
		return err;
	}

	// make sure we don't immediately evict
	dir->rev += dir->rev & 1;

	// set defaults
	dir->off = sizeof(dir->rev);
	dir->etag = 0xffffffff;
	dir->count = 0;
	dir->tail[0] = LFS_BLOCK_NULL;
	dir->tail[1] = LFS_BLOCK_NULL;
	dir->erased = false;
	dir->split = false;

	// don't write out yet, let caller take care of that
	return 0;
}

static int lfs_dir_drop(lfs_t *lfs, lfs_mdir_t *dir, lfs_mdir_t *tail)
{
	// steal state
	int err = lfs_dir_getgstate(lfs, tail, &lfs->gdelta);
	if(err)
	{
		return err;
	}

	// steal tail
	lfs_pair_tole32(tail->tail);
	err = lfs_dir_commit(lfs, dir, LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_TAIL + tail->split, 0x3ff, 8), tail->tail }));
	lfs_pair_fromle32(tail->tail);
	if(err)
	{
		return err;
	}

	return 0;
}

static int lfs_dir_split(lfs_t *lfs,
						 lfs_mdir_t *dir,
						 const struct lfs_mattr *attrs,
						 int attrcount,
						 lfs_mdir_t *source,
						 uint16_t split,
						 uint16_t end)
{
	// create tail directory
	lfs_alloc_ack(lfs);
	lfs_mdir_t tail;
	int err = lfs_dir_alloc(lfs, &tail);
	if(err)
	{
		return err;
	}

	tail.split = dir->split;
	tail.tail[0] = dir->tail[0];
	tail.tail[1] = dir->tail[1];

	err = lfs_dir_compact(lfs, &tail, attrs, attrcount, source, split, end);
	if(err)
	{
		return err;
	}

	dir->tail[0] = tail.pair[0];
	dir->tail[1] = tail.pair[1];
	dir->split = true;

	// update root if needed
	if(lfs_pair_cmp(dir->pair, lfs->root) == 0 && split == 0)
	{
		lfs->root[0] = tail.pair[0];
		lfs->root[1] = tail.pair[1];
	}

	return 0;
}

static int lfs_dir_commit_size(void *p, lfs_tag_t tag, const void *buffer)
{
	lfs_size_t *size = p;
	(void)buffer;

	*size += lfs_tag_dsize(tag);
	return 0;
}

struct lfs_dir_commit_commit
{
	lfs_t *lfs;
	struct lfs_commit *commit;
};

static int lfs_dir_commit_commit(void *p, lfs_tag_t tag, const void *buffer)
{
	struct lfs_dir_commit_commit *commit = p;
	return lfs_dir_commitattr(commit->lfs, commit->commit, tag, buffer);
}

static int lfs_dir_compact(lfs_t *lfs,
						   lfs_mdir_t *dir,
						   const struct lfs_mattr *attrs,
						   int attrcount,
						   lfs_mdir_t *source,
						   uint16_t begin,
						   uint16_t end)
{
	// save some state in case block is bad
	const lfs_block_t oldpair[2] = { dir->pair[0], dir->pair[1] };
	bool relocated = false;
	bool tired = false;

	// should we split?
	while(end - begin > 1)
	{
		// find size
		lfs_size_t size = 0;
		int err = lfs_dir_traverse(lfs,
								   source,
								   0,
								   0xffffffff,
								   attrs,
								   attrcount,
								   LFS_MKTAG(0x400, 0x3ff, 0),
								   LFS_MKTAG(LFS_TYPE_NAME, 0, 0),
								   begin,
								   end,
								   -begin,
								   lfs_dir_commit_size,
								   &size);
		if(err)
		{
			return err;
		}

		// space is complicated, we need room for tail, crc, gstate,
		// cleanup delete, and we cap at half a block to give room
		// for metadata updates.
		if(end - begin < 0xff
		   && size <= lfs_min(lfs->cfg->block_size - 36, lfs_alignup(lfs->cfg->block_size / 2, lfs->cfg->prog_size)))
		{
			break;
		}

		// can't fit, need to split, we should really be finding the
		// largest size that fits with a small binary search, but right now
		// it's not worth the code size
		uint16_t split = (end - begin) / 2;
		err = lfs_dir_split(lfs, dir, attrs, attrcount, source, begin + split, end);
		if(err)
		{
			// if we fail to split, we may be able to overcompact, unless
			// we're too big for even the full block, in which case our
			// only option is to error
			if(err == LFS_ERR_NOSPC && size <= lfs->cfg->block_size - 36)
			{
				break;
			}
			return err;
		}

		end = begin + split;
	}

	// increment revision count
	dir->rev += 1;
	// If our revision count == n * block_cycles, we should force a relocation,
	// this is how littlefs wear-levels at the metadata-pair level. Note that we
	// actually use (block_cycles+1)|1, this is to avoid two corner cases:
	// 1. block_cycles = 1, which would prevent relocations from terminating
	// 2. block_cycles = 2n, which, due to aliasing, would only ever relocate
	//    one metadata block in the pair, effectively making this useless
	if(lfs->cfg->block_cycles > 0 && (dir->rev % ((lfs->cfg->block_cycles + 1) | 1) == 0))
	{
		if(lfs_pair_cmp(dir->pair, (const lfs_block_t[2]){ 0, 1 }) == 0)
		{
			// oh no! we're writing too much to the superblock,
			// should we expand?
			lfs_ssize_t res = lfs_fs_size(lfs);
			if(res < 0)
			{
				return res;
			}

			// do we have extra space? littlefs can't reclaim this space
			// by itself, so expand cautiously
			if((lfs_size_t)res < lfs->cfg->block_count / 2)
			{
				LFS_DEBUG("Expanding superblock at rev %" PRIu32, dir->rev);
				int err = lfs_dir_split(lfs, dir, attrs, attrcount, source, begin, end);
				if(err && err != LFS_ERR_NOSPC)
				{
					return err;
				}

				// welp, we tried, if we ran out of space there's not much
				// we can do, we'll error later if we've become frozen
				if(!err)
				{
					end = begin;
				}
			}
#ifdef LFS_MIGRATE
		}
		else if(lfs->lfs1)
		{
			// do not proactively relocate blocks during migrations, this
			// can cause a number of failure states such: clobbering the
			// v1 superblock if we relocate root, and invalidating directory
			// pointers if we relocate the head of a directory. On top of
			// this, relocations increase the overall complexity of
			// lfs_migration, which is already a delicate operation.
#endif
		}
		else
		{
			// we're writing too much, time to relocate
			tired = true;
			goto relocate;
		}
	}

	// begin loop to commit compaction to blocks until a compact sticks
	while(true)
	{
		{
			// setup commit state
			struct lfs_commit commit = {
				.block = dir->pair[1],
				.off = 0,
				.ptag = 0xffffffff,
				.crc = 0xffffffff,

				.begin = 0,
				.end = lfs->cfg->block_size - 8,
			};

			// erase block to write to
			int err = lfs_bd_erase(lfs, dir->pair[1]);
			if(err)
			{
				if(err == LFS_ERR_CORRUPT)
				{
					goto relocate;
				}
				return err;
			}

			// write out header
			dir->rev = lfs_tole32(dir->rev);
			err = lfs_dir_commitprog(lfs, &commit, &dir->rev, sizeof(dir->rev));
			dir->rev = lfs_fromle32(dir->rev);
			if(err)
			{
				if(err == LFS_ERR_CORRUPT)
				{
					goto relocate;
				}
				return err;
			}

			// traverse the directory, this time writing out all unique tags
			err = lfs_dir_traverse(lfs,
								   source,
								   0,
								   0xffffffff,
								   attrs,
								   attrcount,
								   LFS_MKTAG(0x400, 0x3ff, 0),
								   LFS_MKTAG(LFS_TYPE_NAME, 0, 0),
								   begin,
								   end,
								   -begin,
								   lfs_dir_commit_commit,
								   &(struct lfs_dir_commit_commit){ lfs, &commit });
			if(err)
			{
				if(err == LFS_ERR_CORRUPT)
				{
					goto relocate;
				}
				return err;
			}

			// commit tail, which may be new after last size check
			if(!lfs_pair_isnull(dir->tail))
			{
				lfs_pair_tole32(dir->tail);
				err = lfs_dir_commitattr(lfs, &commit, LFS_MKTAG(LFS_TYPE_TAIL + dir->split, 0x3ff, 8), dir->tail);
				lfs_pair_fromle32(dir->tail);
				if(err)
				{
					if(err == LFS_ERR_CORRUPT)
					{
						goto relocate;
					}
					return err;
				}
			}

			// bring over gstate?
			lfs_gstate_t delta = { 0 };
			if(!relocated)
			{
				lfs_gstate_xor(&delta, &lfs->gdisk);
				lfs_gstate_xor(&delta, &lfs->gstate);
			}
			lfs_gstate_xor(&delta, &lfs->gdelta);
			delta.tag &= ~LFS_MKTAG(0, 0, 0x3ff);

			err = lfs_dir_getgstate(lfs, dir, &delta);
			if(err)
			{
				return err;
			}

			if(!lfs_gstate_iszero(&delta))
			{
				lfs_gstate_tole32(&delta);
				err = lfs_dir_commitattr(lfs, &commit, LFS_MKTAG(LFS_TYPE_MOVESTATE, 0x3ff, sizeof(delta)), &delta);
				if(err)
				{
					if(err == LFS_ERR_CORRUPT)
					{
						goto relocate;
					}
					return err;
				}
			}

			// complete commit with crc
			err = lfs_dir_commitcrc(lfs, &commit);
			if(err)
			{
				if(err == LFS_ERR_CORRUPT)
				{
					goto relocate;
				}
				return err;
			}

			// successful compaction, swap dir pair to indicate most recent
			LFS_ASSERT(commit.off % lfs->cfg->prog_size == 0);
			lfs_pair_swap(dir->pair);
			dir->count = end - begin;
			dir->off = commit.off;
			dir->etag = commit.ptag;
			// update gstate
			lfs->gdelta = (lfs_gstate_t){ 0 };
			if(!relocated)
			{
				lfs->gdisk = lfs->gstate;
			}
		}
		break;

	relocate:
		// commit was corrupted, drop caches and prepare to relocate block
		relocated = true;
		lfs_cache_drop(lfs, &lfs->pcache);
		if(!tired)
		{
			LFS_DEBUG("Bad block at 0x%" PRIx32, dir->pair[1]);
		}

		// can't relocate superblock, filesystem is now frozen
		if(lfs_pair_cmp(dir->pair, (const lfs_block_t[2]){ 0, 1 }) == 0)
		{
			LFS_WARN("Superblock 0x%" PRIx32 " has become unwritable", dir->pair[1]);
			return LFS_ERR_NOSPC;
		}

		// relocate half of pair
		int err = lfs_alloc(lfs, &dir->pair[1]);
		if(err && (err != LFS_ERR_NOSPC || !tired))
		{
			return err;
		}

		tired = false;
		continue;
	}

	if(relocated)
	{
		// update references if we relocated
		LFS_DEBUG("Relocating {0x%" PRIx32 ", 0x%" PRIx32 "} "
				  "-> {0x%" PRIx32 ", 0x%" PRIx32 "}",
				  oldpair[0],
				  oldpair[1],
				  dir->pair[0],
				  dir->pair[1]);
		int err = lfs_fs_relocate(lfs, oldpair, dir->pair);
		if(err)
		{
			return err;
		}
	}

	return 0;
}

static int lfs_dir_commit(lfs_t *lfs, lfs_mdir_t *dir, const struct lfs_mattr *attrs, int attrcount)
{
	// check for any inline files that aren't RAM backed and
	// forcefully evict them, needed for filesystem consistency
	for(lfs_file_t *f = (lfs_file_t *)lfs->mlist; f; f = f->next)
	{
		if(dir != &f->m && lfs_pair_cmp(f->m.pair, dir->pair) == 0 && f->type == LFS_TYPE_REG
		   && (f->flags & LFS_F_INLINE) && f->ctz.size > lfs->cfg->cache_size)
		{
			int err = lfs_file_outline(lfs, f);
			if(err)
			{
				return err;
			}

			err = lfs_file_flush(lfs, f);
			if(err)
			{
				return err;
			}
		}
	}

	// calculate changes to the directory
	lfs_mdir_t olddir = *dir;
	bool hasdelete = false;
	for(int i = 0; i < attrcount; i++)
	{
		if(lfs_tag_type3(attrs[i].tag) == LFS_TYPE_CREATE)
		{
			dir->count += 1;
		}
		else if(lfs_tag_type3(attrs[i].tag) == LFS_TYPE_DELETE)
		{
			LFS_ASSERT(dir->count > 0);
			dir->count -= 1;
			hasdelete = true;
		}
		else if(lfs_tag_type1(attrs[i].tag) == LFS_TYPE_TAIL)
		{
			dir->tail[0] = ((lfs_block_t *)attrs[i].buffer)[0];
			dir->tail[1] = ((lfs_block_t *)attrs[i].buffer)[1];
			dir->split = (lfs_tag_chunk(attrs[i].tag) & 1);
			lfs_pair_fromle32(dir->tail);
		}
	}

	// should we actually drop the directory block?
	if(hasdelete && dir->count == 0)
	{
		lfs_mdir_t pdir;
		int err = lfs_fs_pred(lfs, dir->pair, &pdir);
		if(err && err != LFS_ERR_NOENT)
		{
			*dir = olddir;
			return err;
		}

		if(err != LFS_ERR_NOENT && pdir.split)
		{
			err = lfs_dir_drop(lfs, &pdir, dir);
			if(err)
			{
				*dir = olddir;
				return err;
			}
		}
	}

	if(dir->erased || dir->count >= 0xff)
	{
		// try to commit
		struct lfs_commit commit = {
			.block = dir->pair[0],
			.off = dir->off,
			.ptag = dir->etag,
			.crc = 0xffffffff,

			.begin = dir->off,
			.end = lfs->cfg->block_size - 8,
		};

		// traverse attrs that need to be written out
		lfs_pair_tole32(dir->tail);
		int err = lfs_dir_traverse(lfs,
								   dir,
								   dir->off,
								   dir->etag,
								   attrs,
								   attrcount,
								   0,
								   0,
								   0,
								   0,
								   0,
								   lfs_dir_commit_commit,
								   &(struct lfs_dir_commit_commit){ lfs, &commit });
		lfs_pair_fromle32(dir->tail);
		if(err)
		{
			if(err == LFS_ERR_NOSPC || err == LFS_ERR_CORRUPT)
			{
				goto compact;
			}
			*dir = olddir;
			return err;
		}

		// commit any global diffs if we have any
		lfs_gstate_t delta = { 0 };
		lfs_gstate_xor(&delta, &lfs->gstate);
		lfs_gstate_xor(&delta, &lfs->gdisk);
		lfs_gstate_xor(&delta, &lfs->gdelta);
		delta.tag &= ~LFS_MKTAG(0, 0, 0x3ff);
		if(!lfs_gstate_iszero(&delta))
		{
			err = lfs_dir_getgstate(lfs, dir, &delta);
			if(err)
			{
				*dir = olddir;
				return err;
			}

			lfs_gstate_tole32(&delta);
			err = lfs_dir_commitattr(lfs, &commit, LFS_MKTAG(LFS_TYPE_MOVESTATE, 0x3ff, sizeof(delta)), &delta);
			if(err)
			{
				if(err == LFS_ERR_NOSPC || err == LFS_ERR_CORRUPT)
				{
					goto compact;
				}
				*dir = olddir;
				return err;
			}
		}

		// finalize commit with the crc
		err = lfs_dir_commitcrc(lfs, &commit);
		if(err)
		{
			if(err == LFS_ERR_NOSPC || err == LFS_ERR_CORRUPT)
			{
				goto compact;
			}
			*dir = olddir;
			return err;
		}

		// successful commit, update dir
		LFS_ASSERT(commit.off % lfs->cfg->prog_size == 0);
		dir->off = commit.off;
		dir->etag = commit.ptag;
		// and update gstate
		lfs->gdisk = lfs->gstate;
		lfs->gdelta = (lfs_gstate_t){ 0 };
	}
	else
	{
	compact:
		// fall back to compaction
		lfs_cache_drop(lfs, &lfs->pcache);

		int err = lfs_dir_compact(lfs, dir, attrs, attrcount, dir, 0, dir->count);
		if(err)
		{
			*dir = olddir;
			return err;
		}
	}

	// this complicated bit of logic is for fixing up any active
	// metadata-pairs that we may have affected
	//
	// note we have to make two passes since the mdir passed to
	// lfs_dir_commit could also be in this list, and even then
	// we need to copy the pair so they don't get clobbered if we refetch
	// our mdir.
	for(struct lfs_mlist *d = lfs->mlist; d; d = d->next)
	{
		if(&d->m != dir && lfs_pair_cmp(d->m.pair, olddir.pair) == 0)
		{
			d->m = *dir;
			for(int i = 0; i < attrcount; i++)
			{
				if(lfs_tag_type3(attrs[i].tag) == LFS_TYPE_DELETE && d->id == lfs_tag_id(attrs[i].tag))
				{
					d->m.pair[0] = LFS_BLOCK_NULL;
					d->m.pair[1] = LFS_BLOCK_NULL;
				}
				else if(lfs_tag_type3(attrs[i].tag) == LFS_TYPE_DELETE && d->id > lfs_tag_id(attrs[i].tag))
				{
					d->id -= 1;
					if(d->type == LFS_TYPE_DIR)
					{
						((lfs_dir_t *)d)->pos -= 1;
					}
				}
				else if(lfs_tag_type3(attrs[i].tag) == LFS_TYPE_CREATE && d->id >= lfs_tag_id(attrs[i].tag))
				{
					d->id += 1;
					if(d->type == LFS_TYPE_DIR)
					{
						((lfs_dir_t *)d)->pos += 1;
					}
				}
			}
		}
	}

	for(struct lfs_mlist *d = lfs->mlist; d; d = d->next)
	{
		if(lfs_pair_cmp(d->m.pair, olddir.pair) == 0)
		{
			while(d->id >= d->m.count && d->m.split)
			{
				// we split and id is on tail now
				d->id -= d->m.count;
				int err = lfs_dir_fetch(lfs, &d->m, d->m.tail);
				if(err)
				{
					return err;
				}
			}
		}
	}

	return 0;
}


/// Top level directory operations ///
int lfs_mkdir(lfs_t *lfs, const char *path)
{
	LFS_TRACE("lfs_mkdir(%p, \"%s\")", (void *)lfs, path);
	// deorphan if we haven't yet, needed at most once after poweron
	int err = lfs_fs_forceconsistency(lfs);
	if(err)
	{
		LFS_TRACE("lfs_mkdir -> %d", err);
		return err;
	}

	struct lfs_mlist cwd;
	cwd.next = lfs->mlist;
	uint16_t id;
	err = lfs_dir_find(lfs, &cwd.m, &path, &id);
	if(!(err == LFS_ERR_NOENT && id != 0x3ff))
	{
		LFS_TRACE("lfs_mkdir -> %d", (err < 0) ? err : LFS_ERR_EXIST);
		return (err < 0) ? err : LFS_ERR_EXIST;
	}

	// check that name fits
	lfs_size_t nlen = strlen(path);
	if(nlen > lfs->name_max)
	{
		LFS_TRACE("lfs_mkdir -> %d", LFS_ERR_NAMETOOLONG);
		return LFS_ERR_NAMETOOLONG;
	}

	// build up new directory
	lfs_alloc_ack(lfs);
	lfs_mdir_t dir;
	err = lfs_dir_alloc(lfs, &dir);
	if(err)
	{
		LFS_TRACE("lfs_mkdir -> %d", err);
		return err;
	}

	// find end of list
	lfs_mdir_t pred = cwd.m;
	while(pred.split)
	{
		err = lfs_dir_fetch(lfs, &pred, pred.tail);
		if(err)
		{
			LFS_TRACE("lfs_mkdir -> %d", err);
			return err;
		}
	}

	// setup dir
	lfs_pair_tole32(pred.tail);
	err = lfs_dir_commit(lfs, &dir, LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_SOFTTAIL, 0x3ff, 8), pred.tail }));
	lfs_pair_fromle32(pred.tail);
	if(err)
	{
		LFS_TRACE("lfs_mkdir -> %d", err);
		return err;
	}

	// current block end of list?
	if(cwd.m.split)
	{
		// update tails, this creates a desync
		lfs_fs_preporphans(lfs, +1);

		// it's possible our predecessor has to be relocated, and if
		// our parent is our predecessor's predecessor, this could have
		// caused our parent to go out of date, fortunately we can hook
		// ourselves into littlefs to catch this
		cwd.type = 0;
		cwd.id = 0;
		lfs->mlist = &cwd;

		lfs_pair_tole32(dir.pair);
		err = lfs_dir_commit(lfs, &pred, LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_SOFTTAIL, 0x3ff, 8), dir.pair }));
		lfs_pair_fromle32(dir.pair);
		if(err)
		{
			lfs->mlist = cwd.next;
			LFS_TRACE("lfs_mkdir -> %d", err);
			return err;
		}

		lfs->mlist = cwd.next;
		lfs_fs_preporphans(lfs, -1);
	}

	// now insert into our parent block
	lfs_pair_tole32(dir.pair);
	err = lfs_dir_commit(lfs,
						 &cwd.m,
						 LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_CREATE, id, 0), NULL },
									 { LFS_MKTAG(LFS_TYPE_DIR, id, nlen), path },
									 { LFS_MKTAG(LFS_TYPE_DIRSTRUCT, id, 8), dir.pair },
									 { LFS_MKTAG_IF(!cwd.m.split, LFS_TYPE_SOFTTAIL, 0x3ff, 8), dir.pair }));
	lfs_pair_fromle32(dir.pair);
	if(err)
	{
		LFS_TRACE("lfs_mkdir -> %d", err);
		return err;
	}

	LFS_TRACE("lfs_mkdir -> %d", 0);
	return 0;
}

int lfs_dir_open(lfs_t *lfs, lfs_dir_t *dir, const char *path)
{
	LFS_TRACE("lfs_dir_open(%p, %p, \"%s\")", (void *)lfs, (void *)dir, path);
	lfs_stag_t tag = lfs_dir_find(lfs, &dir->m, &path, NULL);
	if(tag < 0)
	{
		LFS_TRACE("lfs_dir_open -> %" PRId32, tag);
		return tag;
	}

	if(lfs_tag_type3(tag) != LFS_TYPE_DIR)
	{
		LFS_TRACE("lfs_dir_open -> %d", LFS_ERR_NOTDIR);
		return LFS_ERR_NOTDIR;
	}

	lfs_block_t pair[2];
	if(lfs_tag_id(tag) == 0x3ff)
	{
		// handle root dir separately
		pair[0] = lfs->root[0];
		pair[1] = lfs->root[1];
	}
	else
	{
		// get dir pair from parent
		lfs_stag_t res =
			lfs_dir_get(lfs, &dir->m, LFS_MKTAG(0x700, 0x3ff, 0), LFS_MKTAG(LFS_TYPE_STRUCT, lfs_tag_id(tag), 8), pair);
		if(res < 0)
		{
			LFS_TRACE("lfs_dir_open -> %" PRId32, res);
			return res;
		}
		lfs_pair_fromle32(pair);
	}

	// fetch first pair
	int err = lfs_dir_fetch(lfs, &dir->m, pair);
	if(err)
	{
		LFS_TRACE("lfs_dir_open -> %d", err);
		return err;
	}

	// setup entry
	dir->head[0] = dir->m.pair[0];
	dir->head[1] = dir->m.pair[1];
	dir->id = 0;
	dir->pos = 0;

	// add to list of mdirs
	dir->type = LFS_TYPE_DIR;
	dir->next = (lfs_dir_t *)lfs->mlist;
	lfs->mlist = (struct lfs_mlist *)dir;

	LFS_TRACE("lfs_dir_open -> %d", 0);
	return 0;
}

int lfs_dir_close(lfs_t *lfs, lfs_dir_t *dir)
{
	LFS_TRACE("lfs_dir_close(%p, %p)", (void *)lfs, (void *)dir);
	// remove from list of mdirs
	for(struct lfs_mlist **p = &lfs->mlist; *p; p = &(*p)->next)
	{
		if(*p == (struct lfs_mlist *)dir)
		{
			*p = (*p)->next;
			break;
		}
	}

	LFS_TRACE("lfs_dir_close -> %d", 0);
	return 0;
}

int lfs_dir_read(lfs_t *lfs, lfs_dir_t *dir, struct lfs_info *info)
{
	LFS_TRACE("lfs_dir_read(%p, %p, %p)", (void *)lfs, (void *)dir, (void *)info);
	memset(info, 0, sizeof(*info));

	// special offset for '.' and '..'
	if(dir->pos == 0)
	{
		info->type = LFS_TYPE_DIR;
		strcpy(info->name, ".");
		dir->pos += 1;
		LFS_TRACE("lfs_dir_read -> %d", true);
		return true;
	}
	else if(dir->pos == 1)
	{
		info->type = LFS_TYPE_DIR;
		strcpy(info->name, "..");
		dir->pos += 1;
		LFS_TRACE("lfs_dir_read -> %d", true);
		return true;
	}

	while(true)
	{
		if(dir->id == dir->m.count)
		{
			if(!dir->m.split)
			{
				LFS_TRACE("lfs_dir_read -> %d", false);
				return false;
			}

			int err = lfs_dir_fetch(lfs, &dir->m, dir->m.tail);
			if(err)
			{
				LFS_TRACE("lfs_dir_read -> %d", err);
				return err;
			}

			dir->id = 0;
		}

		int err = lfs_dir_getinfo(lfs, &dir->m, dir->id, info);
		if(err && err != LFS_ERR_NOENT)
		{
			LFS_TRACE("lfs_dir_read -> %d", err);
			return err;
		}

		dir->id += 1;
		if(err != LFS_ERR_NOENT)
		{
			break;
		}
	}

	dir->pos += 1;
	LFS_TRACE("lfs_dir_read -> %d", true);
	return true;
}

int lfs_dir_seek(lfs_t *lfs, lfs_dir_t *dir, lfs_off_t off)
{
	LFS_TRACE("lfs_dir_seek(%p, %p, %" PRIu32 ")", (void *)lfs, (void *)dir, off);
	// simply walk from head dir
	int err = lfs_dir_rewind(lfs, dir);
	if(err)
	{
		LFS_TRACE("lfs_dir_seek -> %d", err);
		return err;
	}

	// first two for ./..
	dir->pos = lfs_min(2, off);
	off -= dir->pos;

	// skip superblock entry
	dir->id = (off > 0 && lfs_pair_cmp(dir->head, lfs->root) == 0);

	while(off > 0)
	{
		int diff = lfs_min(dir->m.count - dir->id, off);
		dir->id += diff;
		dir->pos += diff;
		off -= diff;

		if(dir->id == dir->m.count)
		{
			if(!dir->m.split)
			{
				LFS_TRACE("lfs_dir_seek -> %d", LFS_ERR_INVAL);
				return LFS_ERR_INVAL;
			}

			err = lfs_dir_fetch(lfs, &dir->m, dir->m.tail);
			if(err)
			{
				LFS_TRACE("lfs_dir_seek -> %d", err);
				return err;
			}

			dir->id = 0;
		}
	}

	LFS_TRACE("lfs_dir_seek -> %d", 0);
	return 0;
}

lfs_soff_t lfs_dir_tell(lfs_t *lfs, lfs_dir_t *dir)
{
	LFS_TRACE("lfs_dir_tell(%p, %p)", (void *)lfs, (void *)dir);
	(void)lfs;
	LFS_TRACE("lfs_dir_tell -> %" PRId32, dir->pos);
	return dir->pos;
}

int lfs_dir_rewind(lfs_t *lfs, lfs_dir_t *dir)
{
	LFS_TRACE("lfs_dir_rewind(%p, %p)", (void *)lfs, (void *)dir);
	// reload the head dir
	int err = lfs_dir_fetch(lfs, &dir->m, dir->head);
	if(err)
	{
		LFS_TRACE("lfs_dir_rewind -> %d", err);
		return err;
	}

	dir->id = 0;
	dir->pos = 0;
	LFS_TRACE("lfs_dir_rewind -> %d", 0);
	return 0;
}


/// File index list operations ///
static int lfs_ctz_index(lfs_t *lfs, lfs_off_t *off)
{
	lfs_off_t size = *off;
	lfs_off_t b = lfs->cfg->block_size - 2 * 4;
	lfs_off_t i = size / b;
	if(i == 0)
	{
		return 0;
	}

	i = (size - 4 * (lfs_popc(i - 1) + 2)) / b;
	*off = size - b * i - 4 * lfs_popc(i);
	return i;
}

static int lfs_ctz_find(lfs_t *lfs,
						const lfs_cache_t *pcache,
						lfs_cache_t *rcache,
						lfs_block_t head,
						lfs_size_t size,
						lfs_size_t pos,
						lfs_block_t *block,
						lfs_off_t *off)
{
	if(size == 0)
	{
		*block = LFS_BLOCK_NULL;
		*off = 0;
		return 0;
	}

	lfs_off_t current = lfs_ctz_index(lfs, &(lfs_off_t){ size - 1 });
	lfs_off_t target = lfs_ctz_index(lfs, &pos);

	while(current > target)
	{
		lfs_size_t skip = lfs_min(lfs_npw2(current - target + 1) - 1, lfs_ctz(current));

		int err = lfs_bd_read(lfs, pcache, rcache, sizeof(head), head, 4 * skip, &head, sizeof(head));
		head = lfs_fromle32(head);
		if(err)
		{
			return err;
		}

		current -= 1 << skip;
	}

	*block = head;
	*off = pos;
	return 0;
}

static int lfs_ctz_extend(lfs_t *lfs,
						  lfs_cache_t *pcache,
						  lfs_cache_t *rcache,
						  lfs_block_t head,
						  lfs_size_t size,
						  lfs_block_t *block,
						  lfs_off_t *off)
{
	while(true)
	{
		// go ahead and grab a block
		lfs_block_t nblock;
		int err = lfs_alloc(lfs, &nblock);
		if(err)
		{
			return err;
		}

		{
			err = lfs_bd_erase(lfs, nblock);
			if(err)
			{
				if(err == LFS_ERR_CORRUPT)
				{
					goto relocate;
				}
				return err;
			}

			if(size == 0)
			{
				*block = nblock;
				*off = 0;
				return 0;
			}

			lfs_size_t noff = size - 1;
			lfs_off_t index = lfs_ctz_index(lfs, &noff);
			noff = noff + 1;

			// just copy out the last block if it is incomplete
			if(noff != lfs->cfg->block_size)
			{
				for(lfs_off_t i = 0; i < noff; i++)
				{
					uint8_t data;
					err = lfs_bd_read(lfs, NULL, rcache, noff - i, head, i, &data, 1);
					if(err)
					{
						return err;
					}

					err = lfs_bd_prog(lfs, pcache, rcache, true, nblock, i, &data, 1);
					if(err)
					{
						if(err == LFS_ERR_CORRUPT)
						{
							goto relocate;
						}
						return err;
					}
				}

				*block = nblock;
				*off = noff;
				return 0;
			}

			// append block
			index += 1;
			lfs_size_t skips = lfs_ctz(index) + 1;
			lfs_block_t nhead = head;
			for(lfs_off_t i = 0; i < skips; i++)
			{
				nhead = lfs_tole32(nhead);
				err = lfs_bd_prog(lfs, pcache, rcache, true, nblock, 4 * i, &nhead, 4);
				nhead = lfs_fromle32(nhead);
				if(err)
				{
					if(err == LFS_ERR_CORRUPT)
					{
						goto relocate;
					}
					return err;
				}

				if(i != skips - 1)
				{
					err = lfs_bd_read(lfs, NULL, rcache, sizeof(nhead), nhead, 4 * i, &nhead, sizeof(nhead));
					nhead = lfs_fromle32(nhead);
					if(err)
					{
						return err;
					}
				}
			}

			*block = nblock;
			*off = 4 * skips;
			return 0;
		}

	relocate:
		LFS_DEBUG("Bad block at 0x%" PRIx32, nblock);

		// just clear cache and try a new block
		lfs_cache_drop(lfs, pcache);
	}
}

static int lfs_ctz_traverse(lfs_t *lfs,
							const lfs_cache_t *pcache,
							lfs_cache_t *rcache,
							lfs_block_t head,
							lfs_size_t size,
							int (*cb)(void *, lfs_block_t),
							void *data)
{
	if(size == 0)
	{
		return 0;
	}

	lfs_off_t index = lfs_ctz_index(lfs, &(lfs_off_t){ size - 1 });

	while(true)
	{
		int err = cb(data, head);
		if(err)
		{
			return err;
		}

		if(index == 0)
		{
			return 0;
		}

		lfs_block_t heads[2];
		int count = 2 - (index & 1);
		err = lfs_bd_read(lfs, pcache, rcache, count * sizeof(head), head, 0, &heads, count * sizeof(head));
		heads[0] = lfs_fromle32(heads[0]);
		heads[1] = lfs_fromle32(heads[1]);
		if(err)
		{
			return err;
		}

		for(int i = 0; i < count - 1; i++)
		{
			err = cb(data, heads[i]);
			if(err)
			{
				return err;
			}
		}

		head = heads[count - 1];
		index -= count;
	}
}


/// Top level file operations ///
int lfs_file_opencfg(lfs_t *lfs, lfs_file_t *file, const char *path, int flags, const struct lfs_file_config *cfg)
{
	LFS_TRACE("lfs_file_opencfg(%p, %p, \"%s\", %x, %p {"
			  ".buffer=%p, .attrs=%p, .attr_count=%" PRIu32 "})",
			  (void *)lfs,
			  (void *)file,
			  path,
			  flags,
			  (void *)cfg,
			  cfg->buffer,
			  (void *)cfg->attrs,
			  cfg->attr_count);

	// deorphan if we haven't yet, needed at most once after poweron
	if((flags & 3) != LFS_O_RDONLY)
	{
		int err = lfs_fs_forceconsistency(lfs);
		if(err)
		{
			LFS_TRACE("lfs_file_opencfg -> %d", err);
			return err;
		}
	}

	// setup simple file details
	int err;
	file->cfg = cfg;
	file->flags = flags | LFS_F_OPENED;
	file->pos = 0;
	file->off = 0;
	file->cache.buffer = NULL;

	// allocate entry for file if it doesn't exist
	lfs_stag_t tag = lfs_dir_find(lfs, &file->m, &path, &file->id);
	if(tag < 0 && !(tag == LFS_ERR_NOENT && file->id != 0x3ff))
	{
		err = tag;
		goto cleanup;
	}

	// get id, add to list of mdirs to catch update changes
	file->type = LFS_TYPE_REG;
	file->next = (lfs_file_t *)lfs->mlist;
	lfs->mlist = (struct lfs_mlist *)file;

	if(tag == LFS_ERR_NOENT)
	{
		if(!(flags & LFS_O_CREAT))
		{
			err = LFS_ERR_NOENT;
			goto cleanup;
		}

		// check that name fits
		lfs_size_t nlen = strlen(path);
		if(nlen > lfs->name_max)
		{
			err = LFS_ERR_NAMETOOLONG;
			goto cleanup;
		}

		// get next slot and create entry to remember name
		err = lfs_dir_commit(lfs,
							 &file->m,
							 LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_CREATE, file->id, 0), NULL },
										 { LFS_MKTAG(LFS_TYPE_REG, file->id, nlen), path },
										 { LFS_MKTAG(LFS_TYPE_INLINESTRUCT, file->id, 0), NULL }));
		if(err)
		{
			err = LFS_ERR_NAMETOOLONG;
			goto cleanup;
		}

		tag = LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, 0);
	}
	else if(flags & LFS_O_EXCL)
	{
		err = LFS_ERR_EXIST;
		goto cleanup;
	}
	else if(lfs_tag_type3(tag) != LFS_TYPE_REG)
	{
		err = LFS_ERR_ISDIR;
		goto cleanup;
	}
	else if(flags & LFS_O_TRUNC)
	{
		// truncate if requested
		tag = LFS_MKTAG(LFS_TYPE_INLINESTRUCT, file->id, 0);
		file->flags |= LFS_F_DIRTY;
	}
	else
	{
		// try to load what's on disk, if it's inlined we'll fix it later
		tag =
			lfs_dir_get(lfs, &file->m, LFS_MKTAG(0x700, 0x3ff, 0), LFS_MKTAG(LFS_TYPE_STRUCT, file->id, 8), &file->ctz);
		if(tag < 0)
		{
			err = tag;
			goto cleanup;
		}
		lfs_ctz_fromle32(&file->ctz);
	}

	// fetch attrs
	for(unsigned i = 0; i < file->cfg->attr_count; i++)
	{
		if((file->flags & 3) != LFS_O_WRONLY)
		{
			lfs_stag_t res =
				lfs_dir_get(lfs,
							&file->m,
							LFS_MKTAG(0x7ff, 0x3ff, 0),
							LFS_MKTAG(LFS_TYPE_USERATTR + file->cfg->attrs[i].type, file->id, file->cfg->attrs[i].size),
							file->cfg->attrs[i].buffer);
			if(res < 0 && res != LFS_ERR_NOENT)
			{
				err = res;
				goto cleanup;
			}
		}

		if((file->flags & 3) != LFS_O_RDONLY)
		{
			if(file->cfg->attrs[i].size > lfs->attr_max)
			{
				err = LFS_ERR_NOSPC;
				goto cleanup;
			}

			file->flags |= LFS_F_DIRTY;
		}
	}

	// allocate buffer if needed
	if(file->cfg->buffer)
	{
		file->cache.buffer = file->cfg->buffer;
	}
	else
	{
		file->cache.buffer = lfs_malloc(lfs->cfg->cache_size);
		if(!file->cache.buffer)
		{
			err = LFS_ERR_NOMEM;
			goto cleanup;
		}
	}

	// zero to avoid information leak
	lfs_cache_zero(lfs, &file->cache);

	if(lfs_tag_type3(tag) == LFS_TYPE_INLINESTRUCT)
	{
		// load inline files
		file->ctz.head = LFS_BLOCK_INLINE;
		file->ctz.size = lfs_tag_size(tag);
		file->flags |= LFS_F_INLINE;
		file->cache.block = file->ctz.head;
		file->cache.off = 0;
		file->cache.size = lfs->cfg->cache_size;

		// don't always read (may be new/trunc file)
		if(file->ctz.size > 0)
		{
			lfs_stag_t res = lfs_dir_get(lfs,
										 &file->m,
										 LFS_MKTAG(0x700, 0x3ff, 0),
										 LFS_MKTAG(LFS_TYPE_STRUCT, file->id, lfs_min(file->cache.size, 0x3fe)),
										 file->cache.buffer);
			if(res < 0)
			{
				err = res;
				goto cleanup;
			}
		}
	}

	LFS_TRACE("lfs_file_opencfg -> %d", 0);
	return 0;

cleanup:
	// clean up lingering resources
	file->flags |= LFS_F_ERRED;
	lfs_file_close(lfs, file);
	LFS_TRACE("lfs_file_opencfg -> %d", err);
	return err;
}

int lfs_file_open(lfs_t *lfs, lfs_file_t *file, const char *path, int flags)
{
	LFS_TRACE("lfs_file_open(%p, %p, \"%s\", %x)", (void *)lfs, (void *)file, path, flags);
	static const struct lfs_file_config defaults = { 0 };
	int err = lfs_file_opencfg(lfs, file, path, flags, &defaults);
	LFS_TRACE("lfs_file_open -> %d", err);
	return err;
}

int lfs_file_close(lfs_t *lfs, lfs_file_t *file)
{
	LFS_TRACE("lfs_file_close(%p, %p)", (void *)lfs, (void *)file);
	LFS_ASSERT(file->flags & LFS_F_OPENED);

	int err = lfs_file_sync(lfs, file);

	// remove from list of mdirs
	for(struct lfs_mlist **p = &lfs->mlist; *p; p = &(*p)->next)
	{
		if(*p == (struct lfs_mlist *)file)
		{
			*p = (*p)->next;
			break;
		}
	}

	// clean up memory
	if(!file->cfg->buffer)
	{
		lfs_free(file->cache.buffer);
	}

	file->flags &= ~LFS_F_OPENED;
	LFS_TRACE("lfs_file_close -> %d", err);
	return err;
}

static int lfs_file_relocate(lfs_t *lfs, lfs_file_t *file)
{
	LFS_ASSERT(file->flags & LFS_F_OPENED);

	while(true)
	{
		// just relocate what exists into new block
		lfs_block_t nblock;
		int err = lfs_alloc(lfs, &nblock);
		if(err)
		{
			return err;
		}

		err = lfs_bd_erase(lfs, nblock);
		if(err)
		{
			if(err == LFS_ERR_CORRUPT)
			{
				goto relocate;
			}
			return err;
		}

		// either read from dirty cache or disk
		for(lfs_off_t i = 0; i < file->off; i++)
		{
			uint8_t data;
			if(file->flags & LFS_F_INLINE)
			{
				err = lfs_dir_getread(lfs,
									  &file->m,
									  // note we evict inline files before they can be dirty
									  NULL,
									  &file->cache,
									  file->off - i,
									  LFS_MKTAG(0xfff, 0x1ff, 0),
									  LFS_MKTAG(LFS_TYPE_INLINESTRUCT, file->id, 0),
									  i,
									  &data,
									  1);
				if(err)
				{
					return err;
				}
			}
			else
			{
				err = lfs_bd_read(lfs, &file->cache, &lfs->rcache, file->off - i, file->block, i, &data, 1);
				if(err)
				{
					return err;
				}
			}

			err = lfs_bd_prog(lfs, &lfs->pcache, &lfs->rcache, true, nblock, i, &data, 1);
			if(err)
			{
				if(err == LFS_ERR_CORRUPT)
				{
					goto relocate;
				}
				return err;
			}
		}

		// copy over new state of file
		memcpy(file->cache.buffer, lfs->pcache.buffer, lfs->cfg->cache_size);
		file->cache.block = lfs->pcache.block;
		file->cache.off = lfs->pcache.off;
		file->cache.size = lfs->pcache.size;
		lfs_cache_zero(lfs, &lfs->pcache);

		file->block = nblock;
		file->flags |= LFS_F_WRITING;
		return 0;

	relocate:
		LFS_DEBUG("Bad block at 0x%" PRIx32, nblock);

		// just clear cache and try a new block
		lfs_cache_drop(lfs, &lfs->pcache);
	}
}

static int lfs_file_outline(lfs_t *lfs, lfs_file_t *file)
{
	file->off = file->pos;
	lfs_alloc_ack(lfs);
	int err = lfs_file_relocate(lfs, file);
	if(err)
	{
		return err;
	}

	file->flags &= ~LFS_F_INLINE;
	return 0;
}

static int lfs_file_flush(lfs_t *lfs, lfs_file_t *file)
{
	LFS_ASSERT(file->flags & LFS_F_OPENED);

	if(file->flags & LFS_F_READING)
	{
		if(!(file->flags & LFS_F_INLINE))
		{
			lfs_cache_drop(lfs, &file->cache);
		}
		file->flags &= ~LFS_F_READING;
	}

	if(file->flags & LFS_F_WRITING)
	{
		lfs_off_t pos = file->pos;

		if(!(file->flags & LFS_F_INLINE))
		{
			// copy over anything after current branch
			lfs_file_t orig = {
				.ctz.head = file->ctz.head,
				.ctz.size = file->ctz.size,
				.flags = LFS_O_RDONLY | LFS_F_OPENED,
				.pos = file->pos,
				.cache = lfs->rcache,
			};
			lfs_cache_drop(lfs, &lfs->rcache);

			while(file->pos < file->ctz.size)
			{
				// copy over a byte at a time, leave it up to caching
				// to make this efficient
				uint8_t data;
				lfs_ssize_t res = lfs_file_read(lfs, &orig, &data, 1);
				if(res < 0)
				{
					return res;
				}

				res = lfs_file_write(lfs, file, &data, 1);
				if(res < 0)
				{
					return res;
				}

				// keep our reference to the rcache in sync
				if(lfs->rcache.block != LFS_BLOCK_NULL)
				{
					lfs_cache_drop(lfs, &orig.cache);
					lfs_cache_drop(lfs, &lfs->rcache);
				}
			}

			// write out what we have
			while(true)
			{
				int err = lfs_bd_flush(lfs, &file->cache, &lfs->rcache, true);
				if(err)
				{
					if(err == LFS_ERR_CORRUPT)
					{
						goto relocate;
					}
					return err;
				}

				break;

			relocate:
				LFS_DEBUG("Bad block at 0x%" PRIx32, file->block);
				err = lfs_file_relocate(lfs, file);
				if(err)
				{
					return err;
				}
			}
		}
		else
		{
			file->pos = lfs_max(file->pos, file->ctz.size);
		}

		// actual file updates
		file->ctz.head = file->block;
		file->ctz.size = file->pos;
		file->flags &= ~LFS_F_WRITING;
		file->flags |= LFS_F_DIRTY;

		file->pos = pos;
	}

	return 0;
}

int lfs_file_sync(lfs_t *lfs, lfs_file_t *file)
{
	LFS_TRACE("lfs_file_sync(%p, %p)", (void *)lfs, (void *)file);
	LFS_ASSERT(file->flags & LFS_F_OPENED);

	if(file->flags & LFS_F_ERRED)
	{
		// it's not safe to do anything if our file errored
		LFS_TRACE("lfs_file_sync -> %d", 0);
		return 0;
	}

	int err = lfs_file_flush(lfs, file);
	if(err)
	{
		file->flags |= LFS_F_ERRED;
		LFS_TRACE("lfs_file_sync -> %d", err);
		return err;
	}

	if((file->flags & LFS_F_DIRTY) && !lfs_pair_isnull(file->m.pair))
	{
		// update dir entry
		uint16_t type;
		const void *buffer;
		lfs_size_t size;
		struct lfs_ctz ctz;
		if(file->flags & LFS_F_INLINE)
		{
			// inline the whole file
			type = LFS_TYPE_INLINESTRUCT;
			buffer = file->cache.buffer;
			size = file->ctz.size;
		}
		else
		{
			// update the ctz reference
			type = LFS_TYPE_CTZSTRUCT;
			// copy ctz so alloc will work during a relocate
			ctz = file->ctz;
			lfs_ctz_tole32(&ctz);
			buffer = &ctz;
			size = sizeof(ctz);
		}

		// commit file data and attributes
		err = lfs_dir_commit(
			lfs,
			&file->m,
			LFS_MKATTRS({ LFS_MKTAG(type, file->id, size), buffer },
						{ LFS_MKTAG(LFS_FROM_USERATTRS, file->id, file->cfg->attr_count), file->cfg->attrs }));
		if(err)
		{
			file->flags |= LFS_F_ERRED;
			LFS_TRACE("lfs_file_sync -> %d", err);
			return err;
		}

		file->flags &= ~LFS_F_DIRTY;
	}

	LFS_TRACE("lfs_file_sync -> %d", 0);
	return 0;
}

lfs_ssize_t lfs_file_read(lfs_t *lfs, lfs_file_t *file, void *buffer, lfs_size_t size)
{
	LFS_TRACE("lfs_file_read(%p, %p, %p, %" PRIu32 ")", (void *)lfs, (void *)file, buffer, size);
	LFS_ASSERT(file->flags & LFS_F_OPENED);
	LFS_ASSERT((file->flags & 3) != LFS_O_WRONLY);

	uint8_t *data = buffer;
	lfs_size_t nsize = size;

	if(file->flags & LFS_F_WRITING)
	{
		// flush out any writes
		int err = lfs_file_flush(lfs, file);
		if(err)
		{
			LFS_TRACE("lfs_file_read -> %d", err);
			return err;
		}
	}

	if(file->pos >= file->ctz.size)
	{
		// eof if past end
		LFS_TRACE("lfs_file_read -> %d", 0);
		return 0;
	}

	size = lfs_min(size, file->ctz.size - file->pos);
	nsize = size;

	while(nsize > 0)
	{
		// check if we need a new block
		if(!(file->flags & LFS_F_READING) || file->off == lfs->cfg->block_size)
		{
			if(!(file->flags & LFS_F_INLINE))
			{
				int err = lfs_ctz_find(
					lfs, NULL, &file->cache, file->ctz.head, file->ctz.size, file->pos, &file->block, &file->off);
				if(err)
				{
					LFS_TRACE("lfs_file_read -> %d", err);
					return err;
				}
			}
			else
			{
				file->block = LFS_BLOCK_INLINE;
				file->off = file->pos;
			}

			file->flags |= LFS_F_READING;
		}

		// read as much as we can in current block
		lfs_size_t diff = lfs_min(nsize, lfs->cfg->block_size - file->off);
		if(file->flags & LFS_F_INLINE)
		{
			int err = lfs_dir_getread(lfs,
									  &file->m,
									  NULL,
									  &file->cache,
									  lfs->cfg->block_size,
									  LFS_MKTAG(0xfff, 0x1ff, 0),
									  LFS_MKTAG(LFS_TYPE_INLINESTRUCT, file->id, 0),
									  file->off,
									  data,
									  diff);
			if(err)
			{
				LFS_TRACE("lfs_file_read -> %d", err);
				return err;
			}
		}
		else
		{
			int err = lfs_bd_read(lfs, NULL, &file->cache, lfs->cfg->block_size, file->block, file->off, data, diff);
			if(err)
			{
				LFS_TRACE("lfs_file_read -> %d", err);
				return err;
			}
		}

		file->pos += diff;
		file->off += diff;
		data += diff;
		nsize -= diff;
	}

	LFS_TRACE("lfs_file_read -> %" PRId32, size);
	return size;
}

lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file, const void *buffer, lfs_size_t size)
{
	LFS_TRACE("lfs_file_write(%p, %p, %p, %" PRIu32 ")", (void *)lfs, (void *)file, buffer, size);
	LFS_ASSERT(file->flags & LFS_F_OPENED);
	LFS_ASSERT((file->flags & 3) != LFS_O_RDONLY);

	const uint8_t *data = buffer;
	lfs_size_t nsize = size;

	if(file->flags & LFS_F_READING)
	{
		// drop any reads
		int err = lfs_file_flush(lfs, file);
		if(err)
		{
			LFS_TRACE("lfs_file_write -> %d", err);
			return err;
		}
	}

	if((file->flags & LFS_O_APPEND) && file->pos < file->ctz.size)
	{
		file->pos = file->ctz.size;
	}

	if(file->pos + size > lfs->file_max)
	{
		// Larger than file limit?
		LFS_TRACE("lfs_file_write -> %d", LFS_ERR_FBIG);
		return LFS_ERR_FBIG;
	}

	if(!(file->flags & LFS_F_WRITING) && file->pos > file->ctz.size)
	{
		// fill with zeros
		lfs_off_t pos = file->pos;
		file->pos = file->ctz.size;

		while(file->pos < pos)
		{
			lfs_ssize_t res = lfs_file_write(lfs, file, &(uint8_t){ 0 }, 1);
			if(res < 0)
			{
				LFS_TRACE("lfs_file_write -> %" PRId32, res);
				return res;
			}
		}
	}

	if((file->flags & LFS_F_INLINE)
	   && lfs_max(file->pos + nsize, file->ctz.size)
			  > lfs_min(0x3fe, lfs_min(lfs->cfg->cache_size, lfs->cfg->block_size / 8)))
	{
		// inline file doesn't fit anymore
		int err = lfs_file_outline(lfs, file);
		if(err)
		{
			file->flags |= LFS_F_ERRED;
			LFS_TRACE("lfs_file_write -> %d", err);
			return err;
		}
	}

	while(nsize > 0)
	{
		// check if we need a new block
		if(!(file->flags & LFS_F_WRITING) || file->off == lfs->cfg->block_size)
		{
			if(!(file->flags & LFS_F_INLINE))
			{
				if(!(file->flags & LFS_F_WRITING) && file->pos > 0)
				{
					// find out which block we're extending from
					int err = lfs_ctz_find(lfs,
										   NULL,
										   &file->cache,
										   file->ctz.head,
										   file->ctz.size,
										   file->pos - 1,
										   &file->block,
										   &file->off);
					if(err)
					{
						file->flags |= LFS_F_ERRED;
						LFS_TRACE("lfs_file_write -> %d", err);
						return err;
					}

					// mark cache as dirty since we may have read data into it
					lfs_cache_zero(lfs, &file->cache);
				}

				// extend file with new blocks
				lfs_alloc_ack(lfs);
				int err =
					lfs_ctz_extend(lfs, &file->cache, &lfs->rcache, file->block, file->pos, &file->block, &file->off);
				if(err)
				{
					file->flags |= LFS_F_ERRED;
					LFS_TRACE("lfs_file_write -> %d", err);
					return err;
				}
			}
			else
			{
				file->block = LFS_BLOCK_INLINE;
				file->off = file->pos;
			}

			file->flags |= LFS_F_WRITING;
		}

		// program as much as we can in current block
		lfs_size_t diff = lfs_min(nsize, lfs->cfg->block_size - file->off);
		while(true)
		{
			int err = lfs_bd_prog(lfs, &file->cache, &lfs->rcache, true, file->block, file->off, data, diff);
			if(err)
			{
				if(err == LFS_ERR_CORRUPT)
				{
					goto relocate;
				}
				file->flags |= LFS_F_ERRED;
				LFS_TRACE("lfs_file_write -> %d", err);
				return err;
			}

			break;
		relocate:
			err = lfs_file_relocate(lfs, file);
			if(err)
			{
				file->flags |= LFS_F_ERRED;
				LFS_TRACE("lfs_file_write -> %d", err);
				return err;
			}
		}

		file->pos += diff;
		file->off += diff;
		data += diff;
		nsize -= diff;

		lfs_alloc_ack(lfs);
	}

	file->flags &= ~LFS_F_ERRED;
	LFS_TRACE("lfs_file_write -> %" PRId32, size);
	return size;
}

lfs_soff_t lfs_file_seek(lfs_t *lfs, lfs_file_t *file, lfs_soff_t off, int whence)
{
	LFS_TRACE("lfs_file_seek(%p, %p, %" PRId32 ", %d)", (void *)lfs, (void *)file, off, whence);
	LFS_ASSERT(file->flags & LFS_F_OPENED);

	// write out everything beforehand, may be noop if rdonly
	int err = lfs_file_flush(lfs, file);
	if(err)
	{
		LFS_TRACE("lfs_file_seek -> %d", err);
		return err;
	}

	// find new pos
	lfs_off_t npos = file->pos;
	if(whence == LFS_SEEK_SET)
	{
		npos = off;
	}
	else if(whence == LFS_SEEK_CUR)
	{
		npos = file->pos + off;
	}
	else if(whence == LFS_SEEK_END)
	{
		npos = file->ctz.size + off;
	}

	if(npos > lfs->file_max)
	{
		// file position out of range
		LFS_TRACE("lfs_file_seek -> %d", LFS_ERR_INVAL);
		return LFS_ERR_INVAL;
	}

	// update pos
	file->pos = npos;
	LFS_TRACE("lfs_file_seek -> %" PRId32, npos);
	return npos;
}

int lfs_file_truncate(lfs_t *lfs, lfs_file_t *file, lfs_off_t size)
{
	LFS_TRACE("lfs_file_truncate(%p, %p, %" PRIu32 ")", (void *)lfs, (void *)file, size);
	LFS_ASSERT(file->flags & LFS_F_OPENED);
	LFS_ASSERT((file->flags & 3) != LFS_O_RDONLY);

	if(size > LFS_FILE_MAX)
	{
		LFS_TRACE("lfs_file_truncate -> %d", LFS_ERR_INVAL);
		return LFS_ERR_INVAL;
	}

	lfs_off_t pos = file->pos;
	lfs_off_t oldsize = lfs_file_size(lfs, file);
	if(size < oldsize)
	{
		// need to flush since directly changing metadata
		int err = lfs_file_flush(lfs, file);
		if(err)
		{
			LFS_TRACE("lfs_file_truncate -> %d", err);
			return err;
		}

		// lookup new head in ctz skip list
		err = lfs_ctz_find(lfs, NULL, &file->cache, file->ctz.head, file->ctz.size, size, &file->block, &file->off);
		if(err)
		{
			LFS_TRACE("lfs_file_truncate -> %d", err);
			return err;
		}

		file->ctz.head = file->block;
		file->ctz.size = size;
		file->flags |= LFS_F_DIRTY | LFS_F_READING;
	}
	else if(size > oldsize)
	{
		// flush+seek if not already at end
		if(file->pos != oldsize)
		{
			lfs_soff_t res = lfs_file_seek(lfs, file, 0, LFS_SEEK_END);
			if(res < 0)
			{
				LFS_TRACE("lfs_file_truncate -> %" PRId32, res);
				return (int)res;
			}
		}

		// fill with zeros
		while(file->pos < size)
		{
			lfs_ssize_t res = lfs_file_write(lfs, file, &(uint8_t){ 0 }, 1);
			if(res < 0)
			{
				LFS_TRACE("lfs_file_truncate -> %" PRId32, res);
				return (int)res;
			}
		}
	}

	// restore pos
	lfs_soff_t res = lfs_file_seek(lfs, file, pos, LFS_SEEK_SET);
	if(res < 0)
	{
		LFS_TRACE("lfs_file_truncate -> %" PRId32, res);
		return (int)res;
	}

	LFS_TRACE("lfs_file_truncate -> %d", 0);
	return 0;
}

lfs_soff_t lfs_file_tell(lfs_t *lfs, lfs_file_t *file)
{
	LFS_TRACE("lfs_file_tell(%p, %p)", (void *)lfs, (void *)file);
	LFS_ASSERT(file->flags & LFS_F_OPENED);
	(void)lfs;
	LFS_TRACE("lfs_file_tell -> %" PRId32, file->pos);
	return file->pos;
}

int lfs_file_rewind(lfs_t *lfs, lfs_file_t *file)
{
	LFS_TRACE("lfs_file_rewind(%p, %p)", (void *)lfs, (void *)file);
	lfs_soff_t res = lfs_file_seek(lfs, file, 0, LFS_SEEK_SET);
	if(res < 0)
	{
		LFS_TRACE("lfs_file_rewind -> %" PRId32, res);
		return (int)res;
	}

	LFS_TRACE("lfs_file_rewind -> %d", 0);
	return 0;
}

lfs_soff_t lfs_file_size(lfs_t *lfs, lfs_file_t *file)
{
	LFS_TRACE("lfs_file_size(%p, %p)", (void *)lfs, (void *)file);
	LFS_ASSERT(file->flags & LFS_F_OPENED);
	(void)lfs;
	if(file->flags & LFS_F_WRITING)
	{
		LFS_TRACE("lfs_file_size -> %" PRId32, lfs_max(file->pos, file->ctz.size));
		return lfs_max(file->pos, file->ctz.size);
	}
	else
	{
		LFS_TRACE("lfs_file_size -> %" PRId32, file->ctz.size);
		return file->ctz.size;
	}
}


/// General fs operations ///
int lfs_stat(lfs_t *lfs, const char *path, struct lfs_info *info)
{
	LFS_TRACE("lfs_stat(%p, \"%s\", %p)", (void *)lfs, path, (void *)info);
	lfs_mdir_t cwd;
	lfs_stag_t tag = lfs_dir_find(lfs, &cwd, &path, NULL);
	if(tag < 0)
	{
		LFS_TRACE("lfs_stat -> %" PRId32, tag);
		return (int)tag;
	}

	int err = lfs_dir_getinfo(lfs, &cwd, lfs_tag_id(tag), info);
	LFS_TRACE("lfs_stat -> %d", err);
	return err;
}

int lfs_remove(lfs_t *lfs, const char *path)
{
	LFS_TRACE("lfs_remove(%p, \"%s\")", (void *)lfs, path);
	// deorphan if we haven't yet, needed at most once after poweron
	int err = lfs_fs_forceconsistency(lfs);
	if(err)
	{
		LFS_TRACE("lfs_remove -> %d", err);
		return err;
	}

	lfs_mdir_t cwd;
	lfs_stag_t tag = lfs_dir_find(lfs, &cwd, &path, NULL);
	if(tag < 0 || lfs_tag_id(tag) == 0x3ff)
	{
		LFS_TRACE("lfs_remove -> %" PRId32, (tag < 0) ? tag : LFS_ERR_INVAL);
		return (tag < 0) ? (int)tag : LFS_ERR_INVAL;
	}

	struct lfs_mlist dir;
	dir.next = lfs->mlist;
	if(lfs_tag_type3(tag) == LFS_TYPE_DIR)
	{
		// must be empty before removal
		lfs_block_t pair[2];
		lfs_stag_t res =
			lfs_dir_get(lfs, &cwd, LFS_MKTAG(0x700, 0x3ff, 0), LFS_MKTAG(LFS_TYPE_STRUCT, lfs_tag_id(tag), 8), pair);
		if(res < 0)
		{
			LFS_TRACE("lfs_remove -> %" PRId32, res);
			return (int)res;
		}
		lfs_pair_fromle32(pair);

		err = lfs_dir_fetch(lfs, &dir.m, pair);
		if(err)
		{
			LFS_TRACE("lfs_remove -> %d", err);
			return err;
		}

		if(dir.m.count > 0 || dir.m.split)
		{
			LFS_TRACE("lfs_remove -> %d", LFS_ERR_NOTEMPTY);
			return LFS_ERR_NOTEMPTY;
		}

		// mark fs as orphaned
		lfs_fs_preporphans(lfs, +1);

		// I know it's crazy but yes, dir can be changed by our parent's
		// commit (if predecessor is child)
		dir.type = 0;
		dir.id = 0;
		lfs->mlist = &dir;
	}

	// delete the entry
	err = lfs_dir_commit(lfs, &cwd, LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_DELETE, lfs_tag_id(tag), 0), NULL }));
	if(err)
	{
		lfs->mlist = dir.next;
		LFS_TRACE("lfs_remove -> %d", err);
		return err;
	}

	lfs->mlist = dir.next;
	if(lfs_tag_type3(tag) == LFS_TYPE_DIR)
	{
		// fix orphan
		lfs_fs_preporphans(lfs, -1);

		err = lfs_fs_pred(lfs, dir.m.pair, &cwd);
		if(err)
		{
			LFS_TRACE("lfs_remove -> %d", err);
			return err;
		}

		err = lfs_dir_drop(lfs, &cwd, &dir.m);
		if(err)
		{
			LFS_TRACE("lfs_remove -> %d", err);
			return err;
		}
	}

	LFS_TRACE("lfs_remove -> %d", 0);
	return 0;
}

int lfs_rename(lfs_t *lfs, const char *oldpath, const char *newpath)
{
	LFS_TRACE("lfs_rename(%p, \"%s\", \"%s\")", (void *)lfs, oldpath, newpath);

	// deorphan if we haven't yet, needed at most once after poweron
	int err = lfs_fs_forceconsistency(lfs);
	if(err)
	{
		LFS_TRACE("lfs_rename -> %d", err);
		return err;
	}

	// find old entry
	lfs_mdir_t oldcwd;
	lfs_stag_t oldtag = lfs_dir_find(lfs, &oldcwd, &oldpath, NULL);
	if(oldtag < 0 || lfs_tag_id(oldtag) == 0x3ff)
	{
		LFS_TRACE("lfs_rename -> %" PRId32, (oldtag < 0) ? oldtag : LFS_ERR_INVAL);
		return (oldtag < 0) ? (int)oldtag : LFS_ERR_INVAL;
	}

	// find new entry
	lfs_mdir_t newcwd;
	uint16_t newid;
	lfs_stag_t prevtag = lfs_dir_find(lfs, &newcwd, &newpath, &newid);
	if((prevtag < 0 || lfs_tag_id(prevtag) == 0x3ff) && !(prevtag == LFS_ERR_NOENT && newid != 0x3ff))
	{
		LFS_TRACE("lfs_rename -> %" PRId32, (prevtag < 0) ? prevtag : LFS_ERR_INVAL);
		return (prevtag < 0) ? (int)prevtag : LFS_ERR_INVAL;
	}

	// if we're in the same pair there's a few special cases...
	bool samepair = (lfs_pair_cmp(oldcwd.pair, newcwd.pair) == 0);
	uint16_t newoldid = lfs_tag_id(oldtag);

	struct lfs_mlist prevdir;
	prevdir.next = lfs->mlist;
	if(prevtag == LFS_ERR_NOENT)
	{
		// check that name fits
		lfs_size_t nlen = strlen(newpath);
		if(nlen > lfs->name_max)
		{
			LFS_TRACE("lfs_rename -> %d", LFS_ERR_NAMETOOLONG);
			return LFS_ERR_NAMETOOLONG;
		}

		// there is a small chance we are being renamed in the same
		// directory/ to an id less than our old id, the global update
		// to handle this is a bit messy
		if(samepair && newid <= newoldid)
		{
			newoldid += 1;
		}
	}
	else if(lfs_tag_type3(prevtag) != lfs_tag_type3(oldtag))
	{
		LFS_TRACE("lfs_rename -> %d", LFS_ERR_ISDIR);
		return LFS_ERR_ISDIR;
	}
	else if(samepair && newid == newoldid)
	{
		// we're renaming to ourselves??
		LFS_TRACE("lfs_rename -> %d", 0);
		return 0;
	}
	else if(lfs_tag_type3(prevtag) == LFS_TYPE_DIR)
	{
		// must be empty before removal
		lfs_block_t prevpair[2];
		lfs_stag_t res =
			lfs_dir_get(lfs, &newcwd, LFS_MKTAG(0x700, 0x3ff, 0), LFS_MKTAG(LFS_TYPE_STRUCT, newid, 8), prevpair);
		if(res < 0)
		{
			LFS_TRACE("lfs_rename -> %" PRId32, res);
			return (int)res;
		}
		lfs_pair_fromle32(prevpair);

		// must be empty before removal
		err = lfs_dir_fetch(lfs, &prevdir.m, prevpair);
		if(err)
		{
			LFS_TRACE("lfs_rename -> %d", err);
			return err;
		}

		if(prevdir.m.count > 0 || prevdir.m.split)
		{
			LFS_TRACE("lfs_rename -> %d", LFS_ERR_NOTEMPTY);
			return LFS_ERR_NOTEMPTY;
		}

		// mark fs as orphaned
		lfs_fs_preporphans(lfs, +1);

		// I know it's crazy but yes, dir can be changed by our parent's
		// commit (if predecessor is child)
		prevdir.type = 0;
		prevdir.id = 0;
		lfs->mlist = &prevdir;
	}

	if(!samepair)
	{
		lfs_fs_prepmove(lfs, newoldid, oldcwd.pair);
	}

	// move over all attributes
	err = lfs_dir_commit(lfs,
						 &newcwd,
						 LFS_MKATTRS({ LFS_MKTAG_IF(prevtag != LFS_ERR_NOENT, LFS_TYPE_DELETE, newid, 0), NULL },
									 { LFS_MKTAG(LFS_TYPE_CREATE, newid, 0), NULL },
									 { LFS_MKTAG(lfs_tag_type3(oldtag), newid, strlen(newpath)), newpath },
									 { LFS_MKTAG(LFS_FROM_MOVE, newid, lfs_tag_id(oldtag)), &oldcwd },
									 { LFS_MKTAG_IF(samepair, LFS_TYPE_DELETE, newoldid, 0), NULL }));
	if(err)
	{
		lfs->mlist = prevdir.next;
		LFS_TRACE("lfs_rename -> %d", err);
		return err;
	}

	// let commit clean up after move (if we're different! otherwise move
	// logic already fixed it for us)
	if(!samepair && lfs_gstate_hasmove(&lfs->gstate))
	{
		// prep gstate and delete move id
		lfs_fs_prepmove(lfs, 0x3ff, NULL);
		err = lfs_dir_commit(lfs, &oldcwd, LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_DELETE, lfs_tag_id(oldtag), 0), NULL }));
		if(err)
		{
			lfs->mlist = prevdir.next;
			LFS_TRACE("lfs_rename -> %d", err);
			return err;
		}
	}

	lfs->mlist = prevdir.next;
	if(prevtag != LFS_ERR_NOENT && lfs_tag_type3(prevtag) == LFS_TYPE_DIR)
	{
		// fix orphan
		lfs_fs_preporphans(lfs, -1);

		err = lfs_fs_pred(lfs, prevdir.m.pair, &newcwd);
		if(err)
		{
			LFS_TRACE("lfs_rename -> %d", err);
			return err;
		}

		err = lfs_dir_drop(lfs, &newcwd, &prevdir.m);
		if(err)
		{
			LFS_TRACE("lfs_rename -> %d", err);
			return err;
		}
	}

	LFS_TRACE("lfs_rename -> %d", 0);
	return 0;
}

lfs_ssize_t lfs_getattr(lfs_t *lfs, const char *path, uint8_t type, void *buffer, lfs_size_t size)
{
	LFS_TRACE("lfs_getattr(%p, \"%s\", %" PRIu8 ", %p, %" PRIu32 ")", (void *)lfs, path, type, buffer, size);
	lfs_mdir_t cwd;
	lfs_stag_t tag = lfs_dir_find(lfs, &cwd, &path, NULL);
	if(tag < 0)
	{
		LFS_TRACE("lfs_getattr -> %" PRId32, tag);
		return tag;
	}

	uint16_t id = lfs_tag_id(tag);
	if(id == 0x3ff)
	{
		// special case for root
		id = 0;
		int err = lfs_dir_fetch(lfs, &cwd, lfs->root);
		if(err)
		{
			LFS_TRACE("lfs_getattr -> %d", err);
			return err;
		}
	}

	tag = lfs_dir_get(lfs,
					  &cwd,
					  LFS_MKTAG(0x7ff, 0x3ff, 0),
					  LFS_MKTAG(LFS_TYPE_USERATTR + type, id, lfs_min(size, lfs->attr_max)),
					  buffer);
	if(tag < 0)
	{
		if(tag == LFS_ERR_NOENT)
		{
			LFS_TRACE("lfs_getattr -> %d", LFS_ERR_NOATTR);
			return LFS_ERR_NOATTR;
		}

		LFS_TRACE("lfs_getattr -> %" PRId32, tag);
		return tag;
	}

	size = lfs_tag_size(tag);
	LFS_TRACE("lfs_getattr -> %" PRId32, size);
	return size;
}

static int lfs_commitattr(lfs_t *lfs, const char *path, uint8_t type, const void *buffer, lfs_size_t size)
{
	lfs_mdir_t cwd;
	lfs_stag_t tag = lfs_dir_find(lfs, &cwd, &path, NULL);
	if(tag < 0)
	{
		return tag;
	}

	uint16_t id = lfs_tag_id(tag);
	if(id == 0x3ff)
	{
		// special case for root
		id = 0;
		int err = lfs_dir_fetch(lfs, &cwd, lfs->root);
		if(err)
		{
			return err;
		}
	}

	return lfs_dir_commit(lfs, &cwd, LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_USERATTR + type, id, size), buffer }));
}

int lfs_setattr(lfs_t *lfs, const char *path, uint8_t type, const void *buffer, lfs_size_t size)
{
	LFS_TRACE("lfs_setattr(%p, \"%s\", %" PRIu8 ", %p, %" PRIu32 ")", (void *)lfs, path, type, buffer, size);
	if(size > lfs->attr_max)
	{
		LFS_TRACE("lfs_setattr -> %d", LFS_ERR_NOSPC);
		return LFS_ERR_NOSPC;
	}

	int err = lfs_commitattr(lfs, path, type, buffer, size);
	LFS_TRACE("lfs_setattr -> %d", err);
	return err;
}

int lfs_removeattr(lfs_t *lfs, const char *path, uint8_t type)
{
	LFS_TRACE("lfs_removeattr(%p, \"%s\", %" PRIu8 ")", (void *)lfs, path, type);
	int err = lfs_commitattr(lfs, path, type, NULL, 0x3ff);
	LFS_TRACE("lfs_removeattr -> %d", err);
	return err;
}


/// Filesystem operations ///
static int lfs_init(lfs_t *lfs, const struct lfs_config *cfg)
{
	lfs->cfg = cfg;
	int err = 0;

	// validate that the lfs-cfg sizes were initiated properly before
	// performing any arithmetic logics with them
	LFS_ASSERT(lfs->cfg->read_size != 0);
	LFS_ASSERT(lfs->cfg->prog_size != 0);
	LFS_ASSERT(lfs->cfg->cache_size != 0);

	// check that block size is a multiple of cache size is a multiple
	// of prog and read sizes
	LFS_ASSERT(lfs->cfg->cache_size % lfs->cfg->read_size == 0);
	LFS_ASSERT(lfs->cfg->cache_size % lfs->cfg->prog_size == 0);
	LFS_ASSERT(lfs->cfg->block_size % lfs->cfg->cache_size == 0);

	// check that the block size is large enough to fit ctz pointers
	LFS_ASSERT(4 * lfs_npw2(0xffffffff / (lfs->cfg->block_size - 2 * 4)) <= lfs->cfg->block_size);

	// block_cycles = 0 is no longer supported.
	//
	// block_cycles is the number of erase cycles before littlefs evicts
	// metadata logs as a part of wear leveling. Suggested values are in the
	// range of 100-1000, or set block_cycles to -1 to disable block-level
	// wear-leveling.
	LFS_ASSERT(lfs->cfg->block_cycles != 0);


	// setup read cache
	if(lfs->cfg->read_buffer)
	{
		lfs->rcache.buffer = lfs->cfg->read_buffer;
	}
	else
	{
		lfs->rcache.buffer = lfs_malloc(lfs->cfg->cache_size);
		if(!lfs->rcache.buffer)
		{
			err = LFS_ERR_NOMEM;
			goto cleanup;
		}
	}

	// setup program cache
	if(lfs->cfg->prog_buffer)
	{
		lfs->pcache.buffer = lfs->cfg->prog_buffer;
	}
	else
	{
		lfs->pcache.buffer = lfs_malloc(lfs->cfg->cache_size);
		if(!lfs->pcache.buffer)
		{
			err = LFS_ERR_NOMEM;
			goto cleanup;
		}
	}

	// zero to avoid information leaks
	lfs_cache_zero(lfs, &lfs->rcache);
	lfs_cache_zero(lfs, &lfs->pcache);

	// setup lookahead, must be multiple of 64-bits, 32-bit aligned
	LFS_ASSERT(lfs->cfg->lookahead_size > 0);
	LFS_ASSERT(lfs->cfg->lookahead_size % 8 == 0 && (uintptr_t)lfs->cfg->lookahead_buffer % 4 == 0);
	if(lfs->cfg->lookahead_buffer)
	{
		lfs->free.buffer = lfs->cfg->lookahead_buffer;
	}
	else
	{
		lfs->free.buffer = lfs_malloc(lfs->cfg->lookahead_size);
		if(!lfs->free.buffer)
		{
			err = LFS_ERR_NOMEM;
			goto cleanup;
		}
	}

	// check that the size limits are sane
	LFS_ASSERT(lfs->cfg->name_max <= LFS_NAME_MAX);
	lfs->name_max = lfs->cfg->name_max;
	if(!lfs->name_max)
	{
		lfs->name_max = LFS_NAME_MAX;
	}

	LFS_ASSERT(lfs->cfg->file_max <= LFS_FILE_MAX);
	lfs->file_max = lfs->cfg->file_max;
	if(!lfs->file_max)
	{
		lfs->file_max = LFS_FILE_MAX;
	}

	LFS_ASSERT(lfs->cfg->attr_max <= LFS_ATTR_MAX);
	lfs->attr_max = lfs->cfg->attr_max;
	if(!lfs->attr_max)
	{
		lfs->attr_max = LFS_ATTR_MAX;
	}

	// setup default state
	lfs->root[0] = LFS_BLOCK_NULL;
	lfs->root[1] = LFS_BLOCK_NULL;
	lfs->mlist = NULL;
	lfs->seed = 0;
	lfs->gdisk = (lfs_gstate_t){ 0 };
	lfs->gstate = (lfs_gstate_t){ 0 };
	lfs->gdelta = (lfs_gstate_t){ 0 };
#ifdef LFS_MIGRATE
	lfs->lfs1 = NULL;
#endif

	return 0;

cleanup:
	lfs_deinit(lfs);
	return err;
}

static int lfs_deinit(lfs_t *lfs)
{
	// free allocated memory
	if(!lfs->cfg->read_buffer)
	{
		lfs_free(lfs->rcache.buffer);
	}

	if(!lfs->cfg->prog_buffer)
	{
		lfs_free(lfs->pcache.buffer);
	}

	if(!lfs->cfg->lookahead_buffer)
	{
		lfs_free(lfs->free.buffer);
	}

	return 0;
}

int lfs_format(lfs_t *lfs, const struct lfs_config *cfg)
{
	LFS_TRACE("lfs_format(%p, %p {.context=%p, "
			  ".read=%p, .prog=%p, .erase=%p, .sync=%p, "
			  ".read_size=%" PRIu32 ", .prog_size=%" PRIu32 ", "
			  ".block_size=%" PRIu32 ", .block_count=%" PRIu32 ", "
			  ".block_cycles=%" PRIu32 ", .cache_size=%" PRIu32 ", "
			  ".lookahead_size=%" PRIu32 ", .read_buffer=%p, "
			  ".prog_buffer=%p, .lookahead_buffer=%p, "
			  ".name_max=%" PRIu32 ", .file_max=%" PRIu32 ", "
			  ".attr_max=%" PRIu32 "})",
			  (void *)lfs,
			  (void *)cfg,
			  cfg->context,
			  (void *)(uintptr_t)cfg->read,
			  (void *)(uintptr_t)cfg->prog,
			  (void *)(uintptr_t)cfg->erase,
			  (void *)(uintptr_t)cfg->sync,
			  cfg->read_size,
			  cfg->prog_size,
			  cfg->block_size,
			  cfg->block_count,
			  cfg->block_cycles,
			  cfg->cache_size,
			  cfg->lookahead_size,
			  cfg->read_buffer,
			  cfg->prog_buffer,
			  cfg->lookahead_buffer,
			  cfg->name_max,
			  cfg->file_max,
			  cfg->attr_max);
	int err = 0;
	{
		err = lfs_init(lfs, cfg);
		if(err)
		{
			LFS_TRACE("lfs_format -> %d", err);
			return err;
		}

		// create free lookahead
		memset(lfs->free.buffer, 0, lfs->cfg->lookahead_size);
		lfs->free.off = 0;
		lfs->free.size = lfs_min(8 * lfs->cfg->lookahead_size, lfs->cfg->block_count);
		lfs->free.i = 0;
		lfs_alloc_ack(lfs);

		// create root dir
		lfs_mdir_t root;
		err = lfs_dir_alloc(lfs, &root);
		if(err)
		{
			goto cleanup;
		}

		// write one superblock
		lfs_superblock_t superblock = {
			.version = LFS_DISK_VERSION,
			.block_size = lfs->cfg->block_size,
			.block_count = lfs->cfg->block_count,
			.name_max = lfs->name_max,
			.file_max = lfs->file_max,
			.attr_max = lfs->attr_max,
		};

		lfs_superblock_tole32(&superblock);
		err = lfs_dir_commit(lfs,
							 &root,
							 LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_CREATE, 0, 0), NULL },
										 { LFS_MKTAG(LFS_TYPE_SUPERBLOCK, 0, 8), "littlefs" },
										 { LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, sizeof(superblock)), &superblock }));
		if(err)
		{
			goto cleanup;
		}

		// sanity check that fetch works
		err = lfs_dir_fetch(lfs, &root, (const lfs_block_t[2]){ 0, 1 });
		if(err)
		{
			goto cleanup;
		}

		// force compaction to prevent accidentally mounting any
		// older version of littlefs that may live on disk
		root.erased = false;
		err = lfs_dir_commit(lfs, &root, NULL, 0);
		if(err)
		{
			goto cleanup;
		}
	}

cleanup:
	lfs_deinit(lfs);
	LFS_TRACE("lfs_format -> %d", err);
	return err;
}

int lfs_mount(lfs_t *lfs, const struct lfs_config *cfg)
{
	LFS_TRACE("lfs_mount(%p, %p {.context=%p, "
			  ".read=%p, .prog=%p, .erase=%p, .sync=%p, "
			  ".read_size=%" PRIu32 ", .prog_size=%" PRIu32 ", "
			  ".block_size=%" PRIu32 ", .block_count=%" PRIu32 ", "
			  ".block_cycles=%" PRIu32 ", .cache_size=%" PRIu32 ", "
			  ".lookahead_size=%" PRIu32 ", .read_buffer=%p, "
			  ".prog_buffer=%p, .lookahead_buffer=%p, "
			  ".name_max=%" PRIu32 ", .file_max=%" PRIu32 ", "
			  ".attr_max=%" PRIu32 "})",
			  (void *)lfs,
			  (void *)cfg,
			  cfg->context,
			  (void *)(uintptr_t)cfg->read,
			  (void *)(uintptr_t)cfg->prog,
			  (void *)(uintptr_t)cfg->erase,
			  (void *)(uintptr_t)cfg->sync,
			  cfg->read_size,
			  cfg->prog_size,
			  cfg->block_size,
			  cfg->block_count,
			  cfg->block_cycles,
			  cfg->cache_size,
			  cfg->lookahead_size,
			  cfg->read_buffer,
			  cfg->prog_buffer,
			  cfg->lookahead_buffer,
			  cfg->name_max,
			  cfg->file_max,
			  cfg->attr_max);
	int err = lfs_init(lfs, cfg);
	if(err)
	{
		LFS_TRACE("lfs_mount -> %d", err);
		return err;
	}

	// scan directory blocks for superblock and any global updates
	lfs_mdir_t dir = { .tail = { 0, 1 } };
	lfs_block_t cycle = 0;
	while(!lfs_pair_isnull(dir.tail))
	{
		if(cycle >= lfs->cfg->block_count / 2)
		{
			// loop detected
			err = LFS_ERR_CORRUPT;
			goto cleanup;
		}
		cycle += 1;

		// fetch next block in tail list
		lfs_stag_t tag = lfs_dir_fetchmatch(lfs,
											&dir,
											dir.tail,
											LFS_MKTAG(0x7ff, 0x3ff, 0),
											LFS_MKTAG(LFS_TYPE_SUPERBLOCK, 0, 8),
											NULL,
											lfs_dir_find_match,
											&(struct lfs_dir_find_match){ lfs, "littlefs", 8 });
		if(tag < 0)
		{
			err = tag;
			goto cleanup;
		}

		// has superblock?
		if(tag && !lfs_tag_isdelete(tag))
		{
			// update root
			lfs->root[0] = dir.pair[0];
			lfs->root[1] = dir.pair[1];

			// grab superblock
			lfs_superblock_t superblock;
			tag = lfs_dir_get(lfs,
							  &dir,
							  LFS_MKTAG(0x7ff, 0x3ff, 0),
							  LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, sizeof(superblock)),
							  &superblock);
			if(tag < 0)
			{
				err = tag;
				goto cleanup;
			}
			lfs_superblock_fromle32(&superblock);

			// check version
			uint16_t major_version = (0xffff & (superblock.version >> 16));
			uint16_t minor_version = (0xffff & (superblock.version >> 0));
			if((major_version != LFS_DISK_VERSION_MAJOR || minor_version > LFS_DISK_VERSION_MINOR))
			{
				LFS_ERROR("Invalid version v%" PRIu16 ".%" PRIu16, major_version, minor_version);
				err = LFS_ERR_INVAL;
				goto cleanup;
			}

			// check superblock configuration
			if(superblock.name_max)
			{
				if(superblock.name_max > lfs->name_max)
				{
					LFS_ERROR("Unsupported name_max (%" PRIu32 " > %" PRIu32 ")", superblock.name_max, lfs->name_max);
					err = LFS_ERR_INVAL;
					goto cleanup;
				}

				lfs->name_max = superblock.name_max;
			}

			if(superblock.file_max)
			{
				if(superblock.file_max > lfs->file_max)
				{
					LFS_ERROR("Unsupported file_max (%" PRIu32 " > %" PRIu32 ")", superblock.file_max, lfs->file_max);
					err = LFS_ERR_INVAL;
					goto cleanup;
				}

				lfs->file_max = superblock.file_max;
			}

			if(superblock.attr_max)
			{
				if(superblock.attr_max > lfs->attr_max)
				{
					LFS_ERROR("Unsupported attr_max (%" PRIu32 " > %" PRIu32 ")", superblock.attr_max, lfs->attr_max);
					err = LFS_ERR_INVAL;
					goto cleanup;
				}

				lfs->attr_max = superblock.attr_max;
			}
		}

		// has gstate?
		err = lfs_dir_getgstate(lfs, &dir, &lfs->gstate);
		if(err)
		{
			goto cleanup;
		}
	}

	// found superblock?
	if(lfs_pair_isnull(lfs->root))
	{
		err = LFS_ERR_INVAL;
		goto cleanup;
	}

	// update littlefs with gstate
	if(!lfs_gstate_iszero(&lfs->gstate))
	{
		LFS_DEBUG("Found pending gstate 0x%08" PRIx32 "%08" PRIx32 "%08" PRIx32,
				  lfs->gstate.tag,
				  lfs->gstate.pair[0],
				  lfs->gstate.pair[1]);
	}
	lfs->gstate.tag += !lfs_tag_isvalid(lfs->gstate.tag);
	lfs->gdisk = lfs->gstate;

	// setup free lookahead
	lfs_alloc_reset(lfs);

	LFS_TRACE("lfs_mount -> %d", 0);
	return 0;

cleanup:
	lfs_unmount(lfs);
	LFS_TRACE("lfs_mount -> %d", err);
	return err;
}

int lfs_unmount(lfs_t *lfs)
{
	LFS_TRACE("lfs_unmount(%p)", (void *)lfs);
	int err = lfs_deinit(lfs);
	LFS_TRACE("lfs_unmount -> %d", err);
	return err;
}


/// Filesystem filesystem operations ///
int lfs_fs_traverseraw(lfs_t *lfs, int (*cb)(void *data, lfs_block_t block), void *data, bool includeorphans)
{
	// iterate over metadata pairs
	lfs_mdir_t dir = { .tail = { 0, 1 } };

#ifdef LFS_MIGRATE
	// also consider v1 blocks during migration
	if(lfs->lfs1)
	{
		int err = lfs1_traverse(lfs, cb, data);
		if(err)
		{
			return err;
		}

		dir.tail[0] = lfs->root[0];
		dir.tail[1] = lfs->root[1];
	}
#endif

	lfs_block_t cycle = 0;
	while(!lfs_pair_isnull(dir.tail))
	{
		if(cycle >= lfs->cfg->block_count / 2)
		{
			// loop detected
			return LFS_ERR_CORRUPT;
		}
		cycle += 1;

		for(int i = 0; i < 2; i++)
		{
			int err = cb(data, dir.tail[i]);
			if(err)
			{
				return err;
			}
		}

		// iterate through ids in directory
		int err = lfs_dir_fetch(lfs, &dir, dir.tail);
		if(err)
		{
			return err;
		}

		for(uint16_t id = 0; id < dir.count; id++)
		{
			struct lfs_ctz ctz;
			lfs_stag_t tag =
				lfs_dir_get(lfs, &dir, LFS_MKTAG(0x700, 0x3ff, 0), LFS_MKTAG(LFS_TYPE_STRUCT, id, sizeof(ctz)), &ctz);
			if(tag < 0)
			{
				if(tag == LFS_ERR_NOENT)
				{
					continue;
				}
				return tag;
			}
			lfs_ctz_fromle32(&ctz);

			if(lfs_tag_type3(tag) == LFS_TYPE_CTZSTRUCT)
			{
				err = lfs_ctz_traverse(lfs, NULL, &lfs->rcache, ctz.head, ctz.size, cb, data);
				if(err)
				{
					return err;
				}
			}
			else if(includeorphans && lfs_tag_type3(tag) == LFS_TYPE_DIRSTRUCT)
			{
				for(int i = 0; i < 2; i++)
				{
					err = cb(data, (&ctz.head)[i]);
					if(err)
					{
						return err;
					}
				}
			}
		}
	}

	// iterate over any open files
	for(lfs_file_t *f = (lfs_file_t *)lfs->mlist; f; f = f->next)
	{
		if(f->type != LFS_TYPE_REG)
		{
			continue;
		}

		if((f->flags & LFS_F_DIRTY) && !(f->flags & LFS_F_INLINE))
		{
			int err = lfs_ctz_traverse(lfs, &f->cache, &lfs->rcache, f->ctz.head, f->ctz.size, cb, data);
			if(err)
			{
				return err;
			}
		}

		if((f->flags & LFS_F_WRITING) && !(f->flags & LFS_F_INLINE))
		{
			int err = lfs_ctz_traverse(lfs, &f->cache, &lfs->rcache, f->block, f->pos, cb, data);
			if(err)
			{
				return err;
			}
		}
	}

	return 0;
}

int lfs_fs_traverse(lfs_t *lfs, int (*cb)(void *data, lfs_block_t block), void *data)
{
	LFS_TRACE("lfs_fs_traverse(%p, %p, %p)", (void *)lfs, (void *)(uintptr_t)cb, data);
	int err = lfs_fs_traverseraw(lfs, cb, data, true);
	LFS_TRACE("lfs_fs_traverse -> %d", 0);
	return err;
}

static int lfs_fs_pred(lfs_t *lfs, const lfs_block_t pair[2], lfs_mdir_t *pdir)
{
	// iterate over all directory directory entries
	pdir->tail[0] = 0;
	pdir->tail[1] = 1;
	lfs_block_t cycle = 0;
	while(!lfs_pair_isnull(pdir->tail))
	{
		if(cycle >= lfs->cfg->block_count / 2)
		{
			// loop detected
			return LFS_ERR_CORRUPT;
		}
		cycle += 1;

		if(lfs_pair_cmp(pdir->tail, pair) == 0)
		{
			return 0;
		}

		int err = lfs_dir_fetch(lfs, pdir, pdir->tail);
		if(err)
		{
			return err;
		}
	}

	return LFS_ERR_NOENT;
}

struct lfs_fs_parent_match
{
	lfs_t *lfs;
	const lfs_block_t pair[2];
};

static int lfs_fs_parent_match(void *data, lfs_tag_t tag, const void *buffer)
{
	struct lfs_fs_parent_match *find = data;
	lfs_t *lfs = find->lfs;
	const struct lfs_diskoff *disk = buffer;
	(void)tag;

	lfs_block_t child[2];
	int err = lfs_bd_read(
		lfs, &lfs->pcache, &lfs->rcache, lfs->cfg->block_size, disk->block, disk->off, &child, sizeof(child));
	if(err)
	{
		return err;
	}

	lfs_pair_fromle32(child);
	return (lfs_pair_cmp(child, find->pair) == 0) ? LFS_CMP_EQ : LFS_CMP_LT;
}

static lfs_stag_t lfs_fs_parent(lfs_t *lfs, const lfs_block_t pair[2], lfs_mdir_t *parent)
{
	// use fetchmatch with callback to find pairs
	parent->tail[0] = 0;
	parent->tail[1] = 1;
	lfs_block_t cycle = 0;
	while(!lfs_pair_isnull(parent->tail))
	{
		if(cycle >= lfs->cfg->block_count / 2)
		{
			// loop detected
			return LFS_ERR_CORRUPT;
		}
		cycle += 1;

		lfs_stag_t tag = lfs_dir_fetchmatch(lfs,
											parent,
											parent->tail,
											LFS_MKTAG(0x7ff, 0, 0x3ff),
											LFS_MKTAG(LFS_TYPE_DIRSTRUCT, 0, 8),
											NULL,
											lfs_fs_parent_match,
											&(struct lfs_fs_parent_match){ lfs, { pair[0], pair[1] } });
		if(tag && tag != LFS_ERR_NOENT)
		{
			return tag;
		}
	}

	return LFS_ERR_NOENT;
}

static int lfs_fs_relocate(lfs_t *lfs, const lfs_block_t oldpair[2], lfs_block_t newpair[2])
{
	// update internal root
	if(lfs_pair_cmp(oldpair, lfs->root) == 0)
	{
		lfs->root[0] = newpair[0];
		lfs->root[1] = newpair[1];
	}

	// update internally tracked dirs
	for(struct lfs_mlist *d = lfs->mlist; d; d = d->next)
	{
		if(lfs_pair_cmp(oldpair, d->m.pair) == 0)
		{
			d->m.pair[0] = newpair[0];
			d->m.pair[1] = newpair[1];
		}

		if(d->type == LFS_TYPE_DIR && lfs_pair_cmp(oldpair, ((lfs_dir_t *)d)->head) == 0)
		{
			((lfs_dir_t *)d)->head[0] = newpair[0];
			((lfs_dir_t *)d)->head[1] = newpair[1];
		}
	}

	// find parent
	lfs_mdir_t parent;
	lfs_stag_t tag = lfs_fs_parent(lfs, oldpair, &parent);
	if(tag < 0 && tag != LFS_ERR_NOENT)
	{
		return tag;
	}

	if(tag != LFS_ERR_NOENT)
	{
		// update disk, this creates a desync
		lfs_fs_preporphans(lfs, +1);

		// fix pending move in this pair? this looks like an optimization but
		// is in fact _required_ since relocating may outdate the move.
		uint16_t moveid = 0x3ff;
		if(lfs_gstate_hasmovehere(&lfs->gstate, parent.pair))
		{
			moveid = lfs_tag_id(lfs->gstate.tag);
			LFS_DEBUG("Fixing move while relocating "
					  "{0x%" PRIx32 ", 0x%" PRIx32 "} 0x%" PRIx16 "\n",
					  parent.pair[0],
					  parent.pair[1],
					  moveid);
			lfs_fs_prepmove(lfs, 0x3ff, NULL);
			if(moveid < lfs_tag_id(tag))
			{
				tag -= LFS_MKTAG(0, 1, 0);
			}
		}

		lfs_pair_tole32(newpair);
		int err = lfs_dir_commit(
			lfs,
			&parent,
			LFS_MKATTRS({ LFS_MKTAG_IF(moveid != 0x3ff, LFS_TYPE_DELETE, moveid, 0), NULL }, { tag, newpair }));
		lfs_pair_fromle32(newpair);
		if(err)
		{
			return err;
		}

		// next step, clean up orphans
		lfs_fs_preporphans(lfs, -1);
	}

	// find pred
	int err = lfs_fs_pred(lfs, oldpair, &parent);
	if(err && err != LFS_ERR_NOENT)
	{
		return err;
	}

	// if we can't find dir, it must be new
	if(err != LFS_ERR_NOENT)
	{
		// fix pending move in this pair? this looks like an optimization but
		// is in fact _required_ since relocating may outdate the move.
		uint16_t moveid = 0x3ff;
		if(lfs_gstate_hasmovehere(&lfs->gstate, parent.pair))
		{
			moveid = lfs_tag_id(lfs->gstate.tag);
			LFS_DEBUG("Fixing move while relocating "
					  "{0x%" PRIx32 ", 0x%" PRIx32 "} 0x%" PRIx16 "\n",
					  parent.pair[0],
					  parent.pair[1],
					  moveid);
			lfs_fs_prepmove(lfs, 0x3ff, NULL);
		}

		// replace bad pair, either we clean up desync, or no desync occured
		lfs_pair_tole32(newpair);
		err = lfs_dir_commit(lfs,
							 &parent,
							 LFS_MKATTRS({ LFS_MKTAG_IF(moveid != 0x3ff, LFS_TYPE_DELETE, moveid, 0), NULL },
										 { LFS_MKTAG(LFS_TYPE_TAIL + parent.split, 0x3ff, 8), newpair }));
		lfs_pair_fromle32(newpair);
		if(err)
		{
			return err;
		}
	}

	return 0;
}

static void lfs_fs_preporphans(lfs_t *lfs, int8_t orphans)
{
	LFS_ASSERT(lfs_tag_size(lfs->gstate.tag) > 0 || orphans >= 0);
	lfs->gstate.tag += orphans;
	lfs->gstate.tag =
		((lfs->gstate.tag & ~LFS_MKTAG(0x800, 0, 0)) | ((uint32_t)lfs_gstate_hasorphans(&lfs->gstate) << 31));
}

static void lfs_fs_prepmove(lfs_t *lfs, uint16_t id, const lfs_block_t pair[2])
{
	lfs->gstate.tag =
		((lfs->gstate.tag & ~LFS_MKTAG(0x7ff, 0x3ff, 0)) | ((id != 0x3ff) ? LFS_MKTAG(LFS_TYPE_DELETE, id, 0) : 0));
	lfs->gstate.pair[0] = (id != 0x3ff) ? pair[0] : 0;
	lfs->gstate.pair[1] = (id != 0x3ff) ? pair[1] : 0;
}

static int lfs_fs_demove(lfs_t *lfs)
{
	if(!lfs_gstate_hasmove(&lfs->gdisk))
	{
		return 0;
	}

	// Fix bad moves
	LFS_DEBUG("Fixing move {0x%" PRIx32 ", 0x%" PRIx32 "} 0x%" PRIx16,
			  lfs->gdisk.pair[0],
			  lfs->gdisk.pair[1],
			  lfs_tag_id(lfs->gdisk.tag));

	// fetch and delete the moved entry
	lfs_mdir_t movedir;
	int err = lfs_dir_fetch(lfs, &movedir, lfs->gdisk.pair);
	if(err)
	{
		return err;
	}

	// prep gstate and delete move id
	uint16_t moveid = lfs_tag_id(lfs->gdisk.tag);
	lfs_fs_prepmove(lfs, 0x3ff, NULL);
	err = lfs_dir_commit(lfs, &movedir, LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_DELETE, moveid, 0), NULL }));
	if(err)
	{
		return err;
	}

	return 0;
}

static int lfs_fs_deorphan(lfs_t *lfs)
{
	if(!lfs_gstate_hasorphans(&lfs->gstate))
	{
		return 0;
	}

	// Fix any orphans
	lfs_mdir_t pdir = { .split = true, .tail = { 0, 1 } };
	lfs_mdir_t dir;

	// iterate over all directory directory entries
	while(!lfs_pair_isnull(pdir.tail))
	{
		int err = lfs_dir_fetch(lfs, &dir, pdir.tail);
		if(err)
		{
			return err;
		}

		// check head blocks for orphans
		if(!pdir.split)
		{
			// check if we have a parent
			lfs_mdir_t parent;
			lfs_stag_t tag = lfs_fs_parent(lfs, pdir.tail, &parent);
			if(tag < 0 && tag != LFS_ERR_NOENT)
			{
				return tag;
			}

			if(tag == LFS_ERR_NOENT)
			{
				// we are an orphan
				LFS_DEBUG("Fixing orphan {0x%" PRIx32 ", 0x%" PRIx32 "}", pdir.tail[0], pdir.tail[1]);

				err = lfs_dir_drop(lfs, &pdir, &dir);
				if(err)
				{
					return err;
				}

				// refetch tail
				continue;
			}

			lfs_block_t pair[2];
			lfs_stag_t res = lfs_dir_get(lfs, &parent, LFS_MKTAG(0x7ff, 0x3ff, 0), tag, pair);
			if(res < 0)
			{
				return res;
			}
			lfs_pair_fromle32(pair);

			if(!lfs_pair_sync(pair, pdir.tail))
			{
				// we have desynced
				LFS_DEBUG("Fixing half-orphan {0x%" PRIx32 ", 0x%" PRIx32 "} "
						  "-> {0x%" PRIx32 ", 0x%" PRIx32 "}",
						  pdir.tail[0],
						  pdir.tail[1],
						  pair[0],
						  pair[1]);

				lfs_pair_tole32(pair);
				err = lfs_dir_commit(lfs, &pdir, LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_SOFTTAIL, 0x3ff, 8), pair }));
				lfs_pair_fromle32(pair);
				if(err)
				{
					return err;
				}

				// refetch tail
				continue;
			}
		}

		pdir = dir;
	}

	// mark orphans as fixed
	lfs_fs_preporphans(lfs, -lfs_gstate_getorphans(&lfs->gstate));
	return 0;
}

static int lfs_fs_forceconsistency(lfs_t *lfs)
{
	int err = lfs_fs_demove(lfs);
	if(err)
	{
		return err;
	}

	err = lfs_fs_deorphan(lfs);
	if(err)
	{
		return err;
	}

	return 0;
}

static int lfs_fs_size_count(void *p, lfs_block_t block)
{
	(void)block;
	lfs_size_t *size = p;
	*size += 1;
	return 0;
}

lfs_ssize_t lfs_fs_size(lfs_t *lfs)
{
	LFS_TRACE("lfs_fs_size(%p)", (void *)lfs);
	lfs_size_t size = 0;
	int err = lfs_fs_traverseraw(lfs, lfs_fs_size_count, &size, false);
	if(err)
	{
		LFS_TRACE("lfs_fs_size -> %d", err);
		return err;
	}

	LFS_TRACE("lfs_fs_size -> %d", err);
	return size;
}

#ifdef LFS_MIGRATE
////// Migration from littelfs v1 below this //////

/// Version info ///

// Software library version
// Major (top-nibble), incremented on backwards incompatible changes
// Minor (bottom-nibble), incremented on feature additions
#define LFS1_VERSION 0x00010007
#define LFS1_VERSION_MAJOR (0xffff & (LFS1_VERSION >> 16))
#define LFS1_VERSION_MINOR (0xffff & (LFS1_VERSION >> 0))

// Version of On-disk data structures
// Major (top-nibble), incremented on backwards incompatible changes
// Minor (bottom-nibble), incremented on feature additions
#define LFS1_DISK_VERSION 0x00010001
#define LFS1_DISK_VERSION_MAJOR (0xffff & (LFS1_DISK_VERSION >> 16))
#define LFS1_DISK_VERSION_MINOR (0xffff & (LFS1_DISK_VERSION >> 0))


/// v1 Definitions ///

// File types
enum lfs1_type
{
	LFS1_TYPE_REG = 0x11,
	LFS1_TYPE_DIR = 0x22,
	LFS1_TYPE_SUPERBLOCK = 0x2e,
};

typedef struct lfs1
{
	lfs_block_t root[2];
} lfs1_t;

typedef struct lfs1_entry
{
	lfs_off_t off;

	struct lfs1_disk_entry
	{
		uint8_t type;
		uint8_t elen;
		uint8_t alen;
		uint8_t nlen;
		union
		{
			struct
			{
				lfs_block_t head;
				lfs_size_t size;
			} file;
			lfs_block_t dir[2];
		} u;
	} d;
} lfs1_entry_t;

typedef struct lfs1_dir
{
	struct lfs1_dir *next;
	lfs_block_t pair[2];
	lfs_off_t off;

	lfs_block_t head[2];
	lfs_off_t pos;

	struct lfs1_disk_dir
	{
		uint32_t rev;
		lfs_size_t size;
		lfs_block_t tail[2];
	} d;
} lfs1_dir_t;

typedef struct lfs1_superblock
{
	lfs_off_t off;

	struct lfs1_disk_superblock
	{
		uint8_t type;
		uint8_t elen;
		uint8_t alen;
		uint8_t nlen;
		lfs_block_t root[2];
		uint32_t block_size;
		uint32_t block_count;
		uint32_t version;
		char magic[8];
	} d;
} lfs1_superblock_t;


/// Low-level wrappers v1->v2 ///
static void lfs1_crc(uint32_t *crc, const void *buffer, size_t size)
{
	*crc = lfs_crc(*crc, buffer, size);
}

static int lfs1_bd_read(lfs_t *lfs, lfs_block_t block, lfs_off_t off, void *buffer, lfs_size_t size)
{
	// if we ever do more than writes to alternating pairs,
	// this may need to consider pcache
	return lfs_bd_read(lfs, &lfs->pcache, &lfs->rcache, size, block, off, buffer, size);
}

static int lfs1_bd_crc(lfs_t *lfs, lfs_block_t block, lfs_off_t off, lfs_size_t size, uint32_t *crc)
{
	for(lfs_off_t i = 0; i < size; i++)
	{
		uint8_t c;
		int err = lfs1_bd_read(lfs, block, off + i, &c, 1);
		if(err)
		{
			return err;
		}

		lfs1_crc(crc, &c, 1);
	}

	return 0;
}


/// Endian swapping functions ///
static void lfs1_dir_fromle32(struct lfs1_disk_dir *d)
{
	d->rev = lfs_fromle32(d->rev);
	d->size = lfs_fromle32(d->size);
	d->tail[0] = lfs_fromle32(d->tail[0]);
	d->tail[1] = lfs_fromle32(d->tail[1]);
}

static void lfs1_dir_tole32(struct lfs1_disk_dir *d)
{
	d->rev = lfs_tole32(d->rev);
	d->size = lfs_tole32(d->size);
	d->tail[0] = lfs_tole32(d->tail[0]);
	d->tail[1] = lfs_tole32(d->tail[1]);
}

static void lfs1_entry_fromle32(struct lfs1_disk_entry *d)
{
	d->u.dir[0] = lfs_fromle32(d->u.dir[0]);
	d->u.dir[1] = lfs_fromle32(d->u.dir[1]);
}

static void lfs1_entry_tole32(struct lfs1_disk_entry *d)
{
	d->u.dir[0] = lfs_tole32(d->u.dir[0]);
	d->u.dir[1] = lfs_tole32(d->u.dir[1]);
}

static void lfs1_superblock_fromle32(struct lfs1_disk_superblock *d)
{
	d->root[0] = lfs_fromle32(d->root[0]);
	d->root[1] = lfs_fromle32(d->root[1]);
	d->block_size = lfs_fromle32(d->block_size);
	d->block_count = lfs_fromle32(d->block_count);
	d->version = lfs_fromle32(d->version);
}


///// Metadata pair and directory operations ///
static inline lfs_size_t lfs1_entry_size(const lfs1_entry_t *entry)
{
	return 4 + entry->d.elen + entry->d.alen + entry->d.nlen;
}

static int lfs1_dir_fetch(lfs_t *lfs, lfs1_dir_t *dir, const lfs_block_t pair[2])
{
	// copy out pair, otherwise may be aliasing dir
	const lfs_block_t tpair[2] = { pair[0], pair[1] };
	bool valid = false;

	// check both blocks for the most recent revision
	for(int i = 0; i < 2; i++)
	{
		struct lfs1_disk_dir test;
		int err = lfs1_bd_read(lfs, tpair[i], 0, &test, sizeof(test));
		lfs1_dir_fromle32(&test);
		if(err)
		{
			if(err == LFS_ERR_CORRUPT)
			{
				continue;
			}
			return err;
		}

		if(valid && lfs_scmp(test.rev, dir->d.rev) < 0)
		{
			continue;
		}

		if((0x7fffffff & test.size) < sizeof(test) + 4 || (0x7fffffff & test.size) > lfs->cfg->block_size)
		{
			continue;
		}

		uint32_t crc = 0xffffffff;
		lfs1_dir_tole32(&test);
		lfs1_crc(&crc, &test, sizeof(test));
		lfs1_dir_fromle32(&test);
		err = lfs1_bd_crc(lfs, tpair[i], sizeof(test), (0x7fffffff & test.size) - sizeof(test), &crc);
		if(err)
		{
			if(err == LFS_ERR_CORRUPT)
			{
				continue;
			}
			return err;
		}

		if(crc != 0)
		{
			continue;
		}

		valid = true;

		// setup dir in case it's valid
		dir->pair[0] = tpair[(i + 0) % 2];
		dir->pair[1] = tpair[(i + 1) % 2];
		dir->off = sizeof(dir->d);
		dir->d = test;
	}

	if(!valid)
	{
		LFS_ERROR("Corrupted dir pair at {0x%" PRIx32 ", 0x%" PRIx32 "}", tpair[0], tpair[1]);
		return LFS_ERR_CORRUPT;
	}

	return 0;
}

static int lfs1_dir_next(lfs_t *lfs, lfs1_dir_t *dir, lfs1_entry_t *entry)
{
	while(dir->off + sizeof(entry->d) > (0x7fffffff & dir->d.size) - 4)
	{
		if(!(0x80000000 & dir->d.size))
		{
			entry->off = dir->off;
			return LFS_ERR_NOENT;
		}

		int err = lfs1_dir_fetch(lfs, dir, dir->d.tail);
		if(err)
		{
			return err;
		}

		dir->off = sizeof(dir->d);
		dir->pos += sizeof(dir->d) + 4;
	}

	int err = lfs1_bd_read(lfs, dir->pair[0], dir->off, &entry->d, sizeof(entry->d));
	lfs1_entry_fromle32(&entry->d);
	if(err)
	{
		return err;
	}

	entry->off = dir->off;
	dir->off += lfs1_entry_size(entry);
	dir->pos += lfs1_entry_size(entry);
	return 0;
}

/// littlefs v1 specific operations ///
int lfs1_traverse(lfs_t *lfs, int (*cb)(void *, lfs_block_t), void *data)
{
	if(lfs_pair_isnull(lfs->lfs1->root))
	{
		return 0;
	}

	// iterate over metadata pairs
	lfs1_dir_t dir;
	lfs1_entry_t entry;
	lfs_block_t cwd[2] = { 0, 1 };

	while(true)
	{
		for(int i = 0; i < 2; i++)
		{
			int err = cb(data, cwd[i]);
			if(err)
			{
				return err;
			}
		}

		int err = lfs1_dir_fetch(lfs, &dir, cwd);
		if(err)
		{
			return err;
		}

		// iterate over contents
		while(dir.off + sizeof(entry.d) <= (0x7fffffff & dir.d.size) - 4)
		{
			err = lfs1_bd_read(lfs, dir.pair[0], dir.off, &entry.d, sizeof(entry.d));
			lfs1_entry_fromle32(&entry.d);
			if(err)
			{
				return err;
			}

			dir.off += lfs1_entry_size(&entry);
			if((0x70 & entry.d.type) == (0x70 & LFS1_TYPE_REG))
			{
				err = lfs_ctz_traverse(lfs, NULL, &lfs->rcache, entry.d.u.file.head, entry.d.u.file.size, cb, data);
				if(err)
				{
					return err;
				}
			}
		}

		// we also need to check if we contain a threaded v2 directory
		lfs_mdir_t dir2 = { .split = true, .tail = { cwd[0], cwd[1] } };
		while(dir2.split)
		{
			err = lfs_dir_fetch(lfs, &dir2, dir2.tail);
			if(err)
			{
				break;
			}

			for(int i = 0; i < 2; i++)
			{
				err = cb(data, dir2.pair[i]);
				if(err)
				{
					return err;
				}
			}
		}

		cwd[0] = dir.d.tail[0];
		cwd[1] = dir.d.tail[1];

		if(lfs_pair_isnull(cwd))
		{
			break;
		}
	}

	return 0;
}

static int lfs1_moved(lfs_t *lfs, const void *e)
{
	if(lfs_pair_isnull(lfs->lfs1->root))
	{
		return 0;
	}

	// skip superblock
	lfs1_dir_t cwd;
	int err = lfs1_dir_fetch(lfs, &cwd, (const lfs_block_t[2]){ 0, 1 });
	if(err)
	{
		return err;
	}

	// iterate over all directory directory entries
	lfs1_entry_t entry;
	while(!lfs_pair_isnull(cwd.d.tail))
	{
		err = lfs1_dir_fetch(lfs, &cwd, cwd.d.tail);
		if(err)
		{
			return err;
		}

		while(true)
		{
			err = lfs1_dir_next(lfs, &cwd, &entry);
			if(err && err != LFS_ERR_NOENT)
			{
				return err;
			}

			if(err == LFS_ERR_NOENT)
			{
				break;
			}

			if(!(0x80 & entry.d.type) && memcmp(&entry.d.u, e, sizeof(entry.d.u)) == 0)
			{
				return true;
			}
		}
	}

	return false;
}

/// Filesystem operations ///
static int lfs1_mount(lfs_t *lfs, struct lfs1 *lfs1, const struct lfs_config *cfg)
{
	int err = 0;
	{
		err = lfs_init(lfs, cfg);
		if(err)
		{
			return err;
		}

		lfs->lfs1 = lfs1;
		lfs->lfs1->root[0] = LFS_BLOCK_NULL;
		lfs->lfs1->root[1] = LFS_BLOCK_NULL;

		// setup free lookahead
		lfs->free.off = 0;
		lfs->free.size = 0;
		lfs->free.i = 0;
		lfs_alloc_ack(lfs);

		// load superblock
		lfs1_dir_t dir;
		lfs1_superblock_t superblock;
		err = lfs1_dir_fetch(lfs, &dir, (const lfs_block_t[2]){ 0, 1 });
		if(err && err != LFS_ERR_CORRUPT)
		{
			goto cleanup;
		}

		if(!err)
		{
			err = lfs1_bd_read(lfs, dir.pair[0], sizeof(dir.d), &superblock.d, sizeof(superblock.d));
			lfs1_superblock_fromle32(&superblock.d);
			if(err)
			{
				goto cleanup;
			}

			lfs->lfs1->root[0] = superblock.d.root[0];
			lfs->lfs1->root[1] = superblock.d.root[1];
		}

		if(err || memcmp(superblock.d.magic, "littlefs", 8) != 0)
		{
			LFS_ERROR("Invalid superblock at {0x%" PRIx32 ", 0x%" PRIx32 "}", 0, 1);
			err = LFS_ERR_CORRUPT;
			goto cleanup;
		}

		uint16_t major_version = (0xffff & (superblock.d.version >> 16));
		uint16_t minor_version = (0xffff & (superblock.d.version >> 0));
		if((major_version != LFS1_DISK_VERSION_MAJOR || minor_version > LFS1_DISK_VERSION_MINOR))
		{
			LFS_ERROR("Invalid version v%d.%d", major_version, minor_version);
			err = LFS_ERR_INVAL;
			goto cleanup;
		}

		return 0;
	}

cleanup:
	lfs_deinit(lfs);
	return err;
}

static int lfs1_unmount(lfs_t *lfs)
{
	return lfs_deinit(lfs);
}

/// v1 migration ///
int lfs_migrate(lfs_t *lfs, const struct lfs_config *cfg)
{
	LFS_TRACE("lfs_migrate(%p, %p {.context=%p, "
			  ".read=%p, .prog=%p, .erase=%p, .sync=%p, "
			  ".read_size=%" PRIu32 ", .prog_size=%" PRIu32 ", "
			  ".block_size=%" PRIu32 ", .block_count=%" PRIu32 ", "
			  ".block_cycles=%" PRIu32 ", .cache_size=%" PRIu32 ", "
			  ".lookahead_size=%" PRIu32 ", .read_buffer=%p, "
			  ".prog_buffer=%p, .lookahead_buffer=%p, "
			  ".name_max=%" PRIu32 ", .file_max=%" PRIu32 ", "
			  ".attr_max=%" PRIu32 "})",
			  (void *)lfs,
			  (void *)cfg,
			  cfg->context,
			  (void *)(uintptr_t)cfg->read,
			  (void *)(uintptr_t)cfg->prog,
			  (void *)(uintptr_t)cfg->erase,
			  (void *)(uintptr_t)cfg->sync,
			  cfg->read_size,
			  cfg->prog_size,
			  cfg->block_size,
			  cfg->block_count,
			  cfg->block_cycles,
			  cfg->cache_size,
			  cfg->lookahead_size,
			  cfg->read_buffer,
			  cfg->prog_buffer,
			  cfg->lookahead_buffer,
			  cfg->name_max,
			  cfg->file_max,
			  cfg->attr_max);
	struct lfs1 lfs1;
	int err = lfs1_mount(lfs, &lfs1, cfg);
	if(err)
	{
		LFS_TRACE("lfs_migrate -> %d", err);
		return err;
	}

	{
		// iterate through each directory, copying over entries
		// into new directory
		lfs1_dir_t dir1;
		lfs_mdir_t dir2;
		dir1.d.tail[0] = lfs->lfs1->root[0];
		dir1.d.tail[1] = lfs->lfs1->root[1];
		while(!lfs_pair_isnull(dir1.d.tail))
		{
			// iterate old dir
			err = lfs1_dir_fetch(lfs, &dir1, dir1.d.tail);
			if(err)
			{
				goto cleanup;
			}

			// create new dir and bind as temporary pretend root
			err = lfs_dir_alloc(lfs, &dir2);
			if(err)
			{
				goto cleanup;
			}

			dir2.rev = dir1.d.rev;
			dir1.head[0] = dir1.pair[0];
			dir1.head[1] = dir1.pair[1];
			lfs->root[0] = dir2.pair[0];
			lfs->root[1] = dir2.pair[1];

			err = lfs_dir_commit(lfs, &dir2, NULL, 0);
			if(err)
			{
				goto cleanup;
			}

			while(true)
			{
				lfs1_entry_t entry1;
				err = lfs1_dir_next(lfs, &dir1, &entry1);
				if(err && err != LFS_ERR_NOENT)
				{
					goto cleanup;
				}

				if(err == LFS_ERR_NOENT)
				{
					break;
				}

				// check that entry has not been moved
				if(entry1.d.type & 0x80)
				{
					int moved = lfs1_moved(lfs, &entry1.d.u);
					if(moved < 0)
					{
						err = moved;
						goto cleanup;
					}

					if(moved)
					{
						continue;
					}

					entry1.d.type &= ~0x80;
				}

				// also fetch name
				char name[LFS_NAME_MAX + 1];
				memset(name, 0, sizeof(name));
				err = lfs1_bd_read(
					lfs, dir1.pair[0], entry1.off + 4 + entry1.d.elen + entry1.d.alen, name, entry1.d.nlen);
				if(err)
				{
					goto cleanup;
				}

				bool isdir = (entry1.d.type == LFS1_TYPE_DIR);

				// create entry in new dir
				err = lfs_dir_fetch(lfs, &dir2, lfs->root);
				if(err)
				{
					goto cleanup;
				}

				uint16_t id;
				err = lfs_dir_find(lfs, &dir2, &(const char *){ name }, &id);
				if(!(err == LFS_ERR_NOENT && id != 0x3ff))
				{
					err = (err < 0) ? err : LFS_ERR_EXIST;
					goto cleanup;
				}

				lfs1_entry_tole32(&entry1.d);
				err = lfs_dir_commit(
					lfs,
					&dir2,
					LFS_MKATTRS(
						{ LFS_MKTAG(LFS_TYPE_CREATE, id, 0) },
						{ LFS_MKTAG_IF_ELSE(isdir, LFS_TYPE_DIR, id, entry1.d.nlen, LFS_TYPE_REG, id, entry1.d.nlen),
						  name },
						{ LFS_MKTAG_IF_ELSE(isdir,
											LFS_TYPE_DIRSTRUCT,
											id,
											sizeof(entry1.d.u),
											LFS_TYPE_CTZSTRUCT,
											id,
											sizeof(entry1.d.u)),
						  &entry1.d.u }));
				lfs1_entry_fromle32(&entry1.d);
				if(err)
				{
					goto cleanup;
				}
			}

			if(!lfs_pair_isnull(dir1.d.tail))
			{
				// find last block and update tail to thread into fs
				err = lfs_dir_fetch(lfs, &dir2, lfs->root);
				if(err)
				{
					goto cleanup;
				}

				while(dir2.split)
				{
					err = lfs_dir_fetch(lfs, &dir2, dir2.tail);
					if(err)
					{
						goto cleanup;
					}
				}

				lfs_pair_tole32(dir2.pair);
				err = lfs_dir_commit(lfs, &dir2, LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_SOFTTAIL, 0x3ff, 8), dir1.d.tail }));
				lfs_pair_fromle32(dir2.pair);
				if(err)
				{
					goto cleanup;
				}
			}

			// Copy over first block to thread into fs. Unfortunately
			// if this fails there is not much we can do.
			LFS_DEBUG("Migrating {0x%" PRIx32 ", 0x%" PRIx32 "} "
					  "-> {0x%" PRIx32 ", 0x%" PRIx32 "}",
					  lfs->root[0],
					  lfs->root[1],
					  dir1.head[0],
					  dir1.head[1]);

			err = lfs_bd_erase(lfs, dir1.head[1]);
			if(err)
			{
				goto cleanup;
			}

			err = lfs_dir_fetch(lfs, &dir2, lfs->root);
			if(err)
			{
				goto cleanup;
			}

			for(lfs_off_t i = 0; i < dir2.off; i++)
			{
				uint8_t dat;
				err = lfs_bd_read(lfs, NULL, &lfs->rcache, dir2.off, dir2.pair[0], i, &dat, 1);
				if(err)
				{
					goto cleanup;
				}

				err = lfs_bd_prog(lfs, &lfs->pcache, &lfs->rcache, true, dir1.head[1], i, &dat, 1);
				if(err)
				{
					goto cleanup;
				}
			}

			err = lfs_bd_flush(lfs, &lfs->pcache, &lfs->rcache, true);
			if(err)
			{
				goto cleanup;
			}
		}

		// Create new superblock. This marks a successful migration!
		err = lfs1_dir_fetch(lfs, &dir1, (const lfs_block_t[2]){ 0, 1 });
		if(err)
		{
			goto cleanup;
		}

		dir2.pair[0] = dir1.pair[0];
		dir2.pair[1] = dir1.pair[1];
		dir2.rev = dir1.d.rev;
		dir2.off = sizeof(dir2.rev);
		dir2.etag = 0xffffffff;
		dir2.count = 0;
		dir2.tail[0] = lfs->lfs1->root[0];
		dir2.tail[1] = lfs->lfs1->root[1];
		dir2.erased = false;
		dir2.split = true;

		lfs_superblock_t superblock = {
			.version = LFS_DISK_VERSION,
			.block_size = lfs->cfg->block_size,
			.block_count = lfs->cfg->block_count,
			.name_max = lfs->name_max,
			.file_max = lfs->file_max,
			.attr_max = lfs->attr_max,
		};

		lfs_superblock_tole32(&superblock);
		err = lfs_dir_commit(lfs,
							 &dir2,
							 LFS_MKATTRS({ LFS_MKTAG(LFS_TYPE_CREATE, 0, 0) },
										 { LFS_MKTAG(LFS_TYPE_SUPERBLOCK, 0, 8), "littlefs" },
										 { LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, sizeof(superblock)), &superblock }));
		if(err)
		{
			goto cleanup;
		}

		// sanity check that fetch works
		err = lfs_dir_fetch(lfs, &dir2, (const lfs_block_t[2]){ 0, 1 });
		if(err)
		{
			goto cleanup;
		}

		// force compaction to prevent accidentally mounting v1
		dir2.erased = false;
		err = lfs_dir_commit(lfs, &dir2, NULL, 0);
		if(err)
		{
			goto cleanup;
		}
	}

cleanup:
	lfs1_unmount(lfs);
	LFS_TRACE("lfs_migrate -> %d", err);
	return err;
}

#endif
